Contents Calculation and the Number system: An Introduction 2 Standardisation for the use of the Number Line 5 Addition Addition: Progression within Written and Mental Methods The Number Line: Holistic Approach to Calculation (Addition) The Written Formal Method: Partitioned and Expanded Columns 8 9 10 Subtraction Subtraction: Progression within Written and Mental Methods The Number Line: Holistic Approach to Calculation (Subtraction) Counting on Method Formal Written Methods: Expanded and Short Column Method 12 12 14 15 Multiplication Multiplication: Progression within Written and Mental Methods Mathematical Understanding: Conceptual Developmental Framework How do I do a sum like 48 x 27? (Child’s Version) How do I break down a sum like 48 x 27? (Child’s Version) The Number Line: Holistic Approach to Calculation (Multiplication) Progression on to Formal Written Methods 17 19 20 21 22 24 Division Division: Progression within Written and Mental Methods Division: Whole School Approach The Number Line: Holistic Approach to Calculation (Division) Division: Progression of Written Methods 27 28 31 33 Calculation strategies: Summary 36 1 Calculation and the Number System The Numeracy Framework (1999) has, in the school’s opinion, focused on Calculation at the expense of the larger more global concept of Number. As a consequence children have become very proficient at strategies that involve partitioning and use these with a fair degree of competence but this has led to many children seeing Numeracy as a lesson where numbers are manipulated in their constituent parts to produce the answer to a calculation. These are powerful and essential building blocks in a child’s numerical understanding, however its over emphasis has led to a situation where few children see numbers as a whole. Hence 427 is seen as 400, 20 and 7 (or worse still 4,2 and 7) as this has become the precursor to any calculation. However when it comes to a calculation such as 427x12, it may be easier to solve the calculation as 427x10 and 427x2 as opposed to the partitioning method (whether this be in the form of the grid or a written long multiplication method.) The truth is that whilst the framework states that the first question children should ask is “Can I do this in my head?” the children are too readily reverting to partitioning and related pen and paper methods. Through this they are losing a feel for number and it is this true sense of the number system that underpins mathematical understanding. How do we correct this? There probably needs to be greater focus on the teaching of number for the sake of number. The 100 square in the Reception class may not assist the child’s ability to add two digit numbers but it gives children the holistic feel of where a number like 76 fits into the number system. Teachers should be aware that activities like this, whilst not necessarily enhancing the children’s ability to calculate per se, are under-girding children’s understanding of number and the number system as a whole. More importantly there needs to be a change of emphasis on the presentation of written methods to children. The children should meet the written methods through the following progression: 1. The emphasis in any calculation should be mental in the wherever possible and children should always be challenged to tackle the calculation without reverting, in the first instance, to pen and paper. 2. The first written method children should meet in all areas of calculation is the number line. This is because it is a powerful visual tool and gives provides a supportive framework for children to develop their own thinking in “drawing” form. 3. Ultimately children will need to be introduced to the more formal written methods. However these should not be introduced ahead of the number line and other informal recording methods. The danger is that children get “stuck” on this perceived “adult” form of calculation and through this lose the sense of number which they can develop in the earlier strategies outlined above. The number line acts as a good bridging point between the “Mental” and the “Formal” methods of calculation. It is interesting to note that although in Year 2 it is introduced as an introduction to “Pen and Paper methods” in the KS3 strategy it comes under the heading of “Mental Methods”. It is, in a very real sense, a mental method that is enhanced through the visual use of the line. It is incumbent upon us therefore to use it as a method that is supportive of the mental approach and a precursor to the formal written methods. 2 It may well be that the teachers delay the teaching of the written formal methods to a time later than that suggested in the Numeracy framework. This must be viewed as a positive move forward rather than being seen in terms of holding children back. The rationale behind the delay is that children should be kept away from the formal written strand of calculation as it has a natural tendency to narrow mathematical thinking towards partitioning and restricts children’s freedom to work with whole numbers. Also experience has shown that once children learn the “trick” of reducing all number calculations to U+U through partitioning they are reluctant to return to the key question which should be “Can I do this in my head?” When children tackle sums such as 2465 + 999 using the column method, it should alert the teacher to the fact that they may have moved onto the column method too quickly and that children are not seeing the holistic nature of the numbers involved. There is an argument for not teaching some of the written methods at all. Certainly the More Able pupils in Year 6 have proved that in larger calculations involving multiplication and division the number line has proved infinitely more reliable than the more traditional “column method” or the partitioning of the grid. This is an area that the school will need to review as it develops more informal methods. Bearing in mind that no school is an island one major factor that may well impinge on this is the recognition that Secondary schools have an expectation that children will be secure in the written methods and this may disadvantage our own children. However where calculation is taught well, through informal and holistic methods then the introduction of the written methods should not cause undue concern or misunderstanding. An evaluation report commissioned by the government to look at the implementation of the Numeracy strategy found that most children, notably the more able, tended to be overloaded by the wealth of strategies that the old Framework offered. This led to them, at best, choosing inefficient strategies for certain calculations and at worse, confusing strategies themselves. “Schools are recognising, increasingly, the importance of adopting a common approach to the recording and layout of pupils’ work, but much remains to be done to put policies into practice.” (Teaching of Calculation in Primary Schools, A report by HMI, April 2002) It is interesting to note in the light of this that the guidance document (DfES Renewed Numeracy Framework: Calculation 2006) states in the introduction for each of the four rules that: “Children are entitled to be taught and to acquire secure mental methods of calculation and one efficient written method of calculation which they know they can rely on when mental methods are not appropriate.” In one sense we made this decision independently some years ago. The written method chosen was the number line and we should continue to use this as the “one efficient written method of calculation”. This method will form the backbone of the curriculum throughout both Key Stages. Its selection as a foundational strategy was based on the following basis: It allows the children to remain on the “mental calculation” strand for longer. As stated above the number line is a good staging post between mental calculation and the more formal written methods. The Number line is a powerful visual tool The Number line puts children in charge of the calculations they undertake when presented with any given problem. This is more in line with the school’s child centred philosophy. 3 Related to this is the fact that the Number line allows children to explore calculation for themselves and is therefore, by definition, more “emergent” in its teaching approach It has been found (within school) to be the most reliable strategy in terms of accuracy when used with the more able pupils in particular. This may be because it does not have as many steps of calculation as its written counterparts. Something the guidance document recognises when it states… “this expanded method is cumbersome, with six multiplications and a lengthy addition of numbers with different numbers of digits to be carried out.” (DfES Renewed Numeracy Framework: Calculation 2006) 4 Standardisation for the use of the Number Line Basic Guidelines The Number Line provides a visual map for children to build numerical understanding. Therefore wherever possible the visual appearance should attempt to reflect the numbers they represent e.g. the jump of 10 should be 10 times bigger than the jump of one. This allows the child not only to see the Number Line as a calculation tool but simultaneously gives them a “feel” for the size and relation of the number themselves. The totals should be placed along the bottom line whilst the number to be added should be placed above. This allows children to differentiate what it being added and the numbers they are adding on. In multiplication this allows children to see x10 and x10 as x20 rather than x100. For Multiplication and Division they should also include the multiplying factors as this allows them to “check” all aspects of the calculation. 23 x 18 = 414 This should be written out in full i.e. 23x10 not simply x10. They can then check whether they have 18 lots of 23 by totalling the numbers in the jumps. They can check each individual sum by the number above the jump e.g. is 23 x 10 =230 as the sum implies. The bottom numbers are left for the running total in accordance with a standard number line. The children should also be encouraged to include a zero on the number line to confirm the calculation’s start point. Many will place a 23 there believing this to be part of the calculation. Addition The number line should have the numbers to be added across the top and the running totals underneath. 48 + 36 = 84 Subtraction 5 In the first instance the subtraction number line should start on the right with the highest number and decrease to the left. This allows children to visually create the concept that “subtraction is the inverse of addition”. 74 – 27 = 47 However as children move through the school they will be introduced to the “Counting up” method for calculations such as 99-94 as it is a far more appropriate method. This should be linked to the concept of “difference” where the number line facilitates this imagery. Again the numbers being subtracted should be placed on top and the total run along underneath. Multiplication Whereas the Number line could be used for quite basic multiplication methods, it is probably true to say that these should be limited, as the array provides a far more powerful and potent image of multiplication. So whilst the number line might include the following method: 4 x 3 =12 Its use should emphasise recording and concept consolidation rather than a tool for portraying multiplication in a learning context. The use of the number line for the teaching of multiplication should be confined to the “holistic” approach to calculation. Meaning that it uses the first number in each calculation as a whole entity, it is not to be used in conjunction with partitioning, where the grid method and the formal written methods are both more efficient and effective. 234 x 24 6 This method allows flexibility for the child as they are in control of the calculation. They can multiply by 10 or any number they wish if they find it easier. The example above uses two steps of 10 and two steps of two, but could have been done through two steps of 11 if children found it easier. It has fewer steps than methods involving partitioning and consequently children have been proved to gain more accurate answers using this approach. Division Like its counterpart, subtraction, division in the first instance should be calculated from right to left on the line. 1344 ÷ 48 As children move towards the top end of the school they can be taught the principle of “counting up” (as long as there is a secure understanding of the nature of inverse between multiplication and division). Indeed at the top end of Year 6 the children can solve all calculations using this method and in one sense can bypass the need for “division sums” completely. Having said that, although using the number line to “count up” will deliver fast and accurate results in a test situation, the children need a secure knowledge and understanding of a range of division methods and these should be taught alongside the number line method. 7 Addition: Progression within Written and Mental Methods Once the children move into an arena where they need a written method to support their calculation they should be presented with the number line as a means of recording their calculation in written form. (See below The Number Line: The Wyche School Holistic approach to calculation) The formal written column methods outlined later should be reserved until Year 5 when the children should be introduced to the method of partitioned and expanded columns. The delay in the more formal approach is so that true understanding can be secured and the number line developed as the children’s “default” strategy. This should not hinder more able children in lower year groups undertaking rigorous and challenging tasks in the area of addition, it should simply lead to them developing a wealth of efficient mental strategies to solve a range of calculations. The Number Line: The Wyche School Holistic Approach to Calculation (Addition) Stage 1: Basic Introduction to Number Line The number line is a powerful visual tool to aid the calculation process Stage 1 The concept of the number line is introduced and the two numbers added. 8 + 7 = 15 Stage 2: Partitioning (TU) Stage 2 This calculation allows secure consolidation of the use of the tens in addition 32+12=44 The main feature here is for children to gain confidence in the partitioning and breaking down of numbers into their constituent parts (e.g. Tens and Units) The addition is undertaken using these constituent parts without further breaking down the numbers This consolidates the basic pattern of adding 10 i.e. 32 + 10 = 42 Stage 3: Partitioning (Bridging TU) The empty number line helps to record the steps on the way to calculating the total. The examples here show “bridging through a ten” this builds on work undertaken above where simple partitioning of the additional number is used. Stage 3 Steps in addition can be recorded on a number line. The steps often bridge through a multiple of 10. 8 + 7 = 15 48 + 36 = 84 or: 8 Stage 4: Half Partitioning (HTU) Before moving onto larger numbers the children should return to the number line. There is a danger that once the children understand that partitioning can reduce any sum to a series of U+U calculations then they may well lose sight of the sense of number. Stage 4 256+226=482 9 10 The Written Formal Method: Partitioned and Expanded Columns (These methods to be taught in Years 5 and 6 only) Stage 1: Partitioning using number (TU) The teacher may wish the children to record their partitioning in number form. Stage 1 Record steps in addition using partitioning: 47 + 76 = 47 + 70 + 6 = 117 + 6 = 123 47 + 76 = 40 + 70 + 7 + 6 = 110 + 13 = 123 Stage 2: Partitioned Columns (TU) Partitioning both numbers into tens and ones mirrors the column method where ones are placed under ones and tens under tens. This also links to mental methods. Stage 2 Partitioned numbers are then written under one another: 47 40 7 76 70 6 110 13 123 Stage 3: Expanded Columns (TU) Stage 3 Write the numbers in columns. Adding the tens first: 47 76 110 13 123 Move on to a layout showing the addition of the tens to the tens and the ones to the ones separately. To find the partial sums either the tens or the ones can be added first, and the total of the partial sums can be found by adding them in any order. As children gain confidence, ask them to start by adding the ones digits first always. The addition of the tens in the calculation 47 + 76 is described in the words ‘forty plus seventy equals one hundred and ten’, stressing the link to the related fact ‘four plus seven equals eleven’. The expanded method leads children to the more compact method so that they understand its structure and efficiency. Stage 4: Column Method (TU) In this method, recording is reduced further. Carry digits are recorded below the line, using the words ‘carry ten’ or ‘carry one hundred’, not ‘carry one’. Adding the ones first: 47 76 13 110 123 Discuss how adding the ones first gives the same answer as adding the tens first. Refine over time to adding the ones digits first consistently. Stage 4 47 76 123 11 Column addition remains efficient when used with larger whole numbers and decimals. Once learned, the method is quick and reliable. 11 Stage 5: Column Method (HTU) The children should have a clear understanding of the numbers behind the calculation. They should therefore know that the column method is not an “efficient or effective method for sums such as 234+99. Similarly they should still be encouraged to ask the question “Can I do this in my head?” Stage 6: Column Method (TH H T U) The children could move straight onto the column method for larger numbers when it is felt that they are fully conversant with the rationale behind the column method. That is: 1. They have a strong sense of place value and are not seeing the sum in the context of a series of U+U sums in a variety of columns. 2. They are able to estimate accurately the calculation they are about to undertake because they have a “feel” for the size of the numbers involved. 3. Also they should be dextrous in their use of more appropriate strategies for certain calculations. e.g. 2458+999 should be seen as a mental calculation. Stage 5 258 87 345 366 458 824 11 11 Stage 6 2345 +1467 3812 34,568 24,243 58,811 12 Subtraction: Progression within Written and Mental Methods Like its addition counterpart the children should be introduced to the numberline as the primary form of written recording. The numbers should be used holistically; namely that in 278-123, the 278 remains one number whilst the 100, 20 and 3 are partitioned to create the calculation. A further development in subtraction is the “Counting up method”. Children will come to see that in a calculation such as 302-298, the most effective and efficient method is “Counting on”. However this is a development and should be taught once the principles of subtraction on a number line are secure. This is to allow children a true understanding of what “taking away” actually means rather than simply presenting them with an easier option for a given calculation. The Number Line: The Wyche School Holistic Approach to Calculation (Subtraction) Stage 1: Using the empty number line Basic Introduction to Number Line The number line is a powerful visual tool to aid the calculation process Stage 1 The concept of the number line is introduced and the two numbers added. 15 - 7 = 8 Stage 2: Half Partitioning (TU) The main feature here is for children to gain confidence in the partitioning and breaking down of numbers into their constituent parts (e.g. Tens and Units) The subtraction is undertaken using these constituent parts without further breaking down the numbers Stage 2 The use of the “whole 10” allows for consolidation of the place value concept in subtraction 24 – 12 = 12 Subtraction can be recorded using partitioning: 74 – 27 = 74 – 20 – 7 = 54 – 7 = 47 74 – 27 = 70 + 4 – 20 – 7 = 60 + 14 – 20 – 7 = 40 + 7 This requires children to subtract a single-digit number or a multiple of 10 from a two-digit number mentally. The method of recording links to counting back on the number line. This consolidates the basic pattern of subtraction of 10 i.e. 24 - 10 = 14 Stage 3: Half Partitioning (Bridging TU) The empty number line helps to record or explain the steps in mental subtraction Steps in subtraction can be recorded on a number line. The steps often bridge through a multiple of 10. 15 – 7 = 8 13 A calculation like 74 – 27 can be recorded by counting back 27 from 74 to reach 47. 74 – 27 = 47 worked by counting back: The steps may be recorded in a different order: or combined: Stage 4: Half Partitioning (HTU) The same principle applies with larger numbers. The primary number remains intact and the digits of the second number are subtracted from it. These should be used in a manner that expresses their value e.g. 300 is 300 not 2. Stage 4 568 – 344 = 224 Stage 5: Half Partitioning (HTU) An Alternative to Decomposition Stage 5: Half Partitioning (HTU) An Alternative to Decomposition 543 – 378 = 165 There are issues with this method when it comes to the secondary number being larger than the primary, however the solution (which involves bridging of “real” numbers) has the ability to develop greater mathematical understanding than its paper based decomposition counterpart, which focuses on more abstract strategies. The solution for most children will lie on the process of bridging as illustrated in the second of the two sums opposite. 543 – 378 with bridging 14 Counting on Method When the concept of subtraction is firmly embedded, the children may be taught the “Counting On” method as a means of consolidating the fact that addition is the inverse of subtraction. The children should develop a good understanding of when the “Counting On” might be a more appropriate strategy e.g. in a sum such as 304-298 where the numbers are close together. It will also consolidate the concept of “difference”. It should not be taught in isolation as an alternative ‘easier’ method to subtraction. The Counting on Method Stage 1: Counting Up Method (TU) This introduces the children to the presentation of the “‘Counting On” method within the context of a numberline The teaching emphasis should be upon the concept of “difference” Stage 2: Partitioning (Bridging TU) with the Counting On Method Stage 2 74 – 47 = 27 The Counting on Method can be combined with the bridging of tens Stage 3: Partitioning but combining steps Stage 1 44 – 12 = 32 The number of rows (or steps) can be reduced by combining steps. With two-digit numbers, this requires children to be able to work out the answer to a calculation such as 30 + = 74 mentally. Stage 3 74 – 47 = 27 Stage 4: Partitioning (HTU) With three-digit numbers the number of steps can again be reduced, provided that children are able to work out answers to calculations such as 178 + = 200 and 200 + = 326 mentally. The most compact form of recording remains reasonably efficient. Stage 4 Stage 5: Partitioning Decimals Stage 5 or: The method can be used with decimals where no more than three columns are required. However, it becomes less efficient when more than three columns are needed. or: 15 Formal Written Methods: The Expanded and Short Column Method There is a recognition in the Renewed framework paper on Calculation that: Partitioning the numbers into tens and ones and writing one under the other mirrors the column method, where ones are placed under ones and tens under tens. This does not link directly to mental methods of counting back or up but parallels the partitioning method for addition. It also relies on secure mental skills.” If this is so then teachers should not be overly quick to introduce the column method to children as they will, by the Framework’s own admission, be introducing a new conceptual form of recording that the children have not yet undertaken. The children should therefore remain using the number line and exploring the numerical concepts thoroughly before being introduced to the column method. The school has made a policy decision that the column method will be taught in Year 6. The rationale for this is that the column method involves a greater abstraction of number and should therefore only be taught once the more fundamental concepts are totally secure. This policy will allow children both the freedom and the time to develop a range of mental strategies and a depth of understanding in the concept. The column method should be seen as an extension activity rather than a strategy taught alongside its mental counterpart. There is an argument that some calculations (basically those that do not involve decomposition e.g. 784-253) are more straightforward when presented through the column method than the numberline. This is true, however the primary question related to all sums should be “Can I do this in my head?” The answer to that question should be “Yes” and to that end the children should therefore not be using any written method to solve such a calculation. Progression for teaching the Column Method: The text is taken from the Framework Guidance (These methods to be taught in Year 6 only) Expanded layout, leading to column method • Partitioning the numbers into tens and ones and writing one under the other mirrors the column method, where ones are placed under ones and tens under tens. • This does not link directly to mental methods of counting back or up but parallels the partitioning method for addition. It also relies on secure mental skills. • The expanded method leads children to the more compact method so that they understand its structure and efficiency. The amount of time that should be spent teaching and practising the expanded method will depend on how secure the children are in their recall of number facts and with partitioning. Partitioned numbers are then written under one another: Example: 74 − 27 70 4 20 7 60 6 14 14 70 4 20 7 40 7 7 4 27 4 7 Example: 741 − 367 700 40 1 300 60 7 600 130 11 700 40 1 300 60 7 300 70 4 6 13 11 7 41 3 67 3 74 16 The expanded method for three-digit numbers Example: 563 − 241, no adjustment or decomposition needed Expanded method leading to 563 500 60 3 241 200 40 1 322 300 20 2 Start by subtracting the ones, then the tens, then the hundreds. Refer to subtracting the tens, for example, by saying ‘sixty take away forty’, not ‘six take away four’. Example: 563 − 271, adjustment from the hundreds to the tens, or partitioning the hundreds 500 60 3 200 70 1 400 160 3 200 70 1 200 90 2 400 160 500 60 3 200 70 1 200 90 2 4 16 5 63 2 71 2 92 Begin by reading aloud the number from which we are subtracting: ‘five hundred and sixty-three’. Then discuss the hundreds, tens and ones components of the number, and how 500 + 60 can be partitioned into 400 + 160. The subtraction of the tens becomes ‘160 minus 70’, an application of subtraction of multiples of ten. Example: 563 − 278, adjustment from the hundreds to the tens and the tens to the ones 500 60 3 400 150 13 200 70 8 200 70 8 200 80 5 400 500 150 50 13 13 500 60 3 200 70 8 200 80 5 4 15 13 5 6 3 278 285 Here both the tens and the ones digits to be subtracted are bigger than both the tens and the ones digits you are subtracting from. Discuss how 60 + 3 is partitioned into 50 + 13, and then how 500 + 50 can be partitioned into 400 + 150, and how this helps when subtracting. Example: 503 − 278, dealing with zeros when adjusting 500 0 3 200 70 8 400 90 13 200 70 8 200 20 5 400 400 90 100 13 3 500 0 3 200 70 8 200 20 5 4 9 13 5 0 3 278 2 25 Here 0 acts as a place holder for the tens. The adjustment has to be done in two stages. First the 500 + 0 is partitioned into 400 + 100 and then the 100 + 3 is partitioned into 90 + 13. 17 Multiplication: Progression within Written and Mental Methods It is interesting to note that in both the old framework and in the guidance provided with the new framework there is no requirement for the children to undertake any written calculations in multiplication before Year 4. All calculations including those such as 32 x 3 = 96 are to be worked out mentally. This allows the children to gain a good sense of calculation using the “whole number” and prevents both the early use of partitioning and the potential problem of children seeing numbers over 10 as a series of digits as opposed to a number in its own right. The use of the number line is the school’s preferred strategy for calculation in multiplication. The rationale for this is as follows: 1. 2. 3. 4. 5. The numberline is used in conjunction with the school’s “half partitioning” strategy. This allows children to calculate in real numbers, rather than reducing each sum to a series of unit calculations. (See Appendix: The Partitioning Predicament) This gives them a “feel for number” which is so crucial in terms of their overall numerical understanding. Related to this the school has undertaken a brief study of the elements of calculation. (See Appendix: Elements of Calculation) Whilst it may be true that in certain contexts and certain scenarios other strategies may be more efficient and/or effective in the short term, the numberline remains the one strategy that hits nearly all the calculation elements every time. The numberline is a very powerful visual tool and children have testified to the fact that it greatly assists both their ability to calculate accurately and their conceptual understanding of number calculation It has proven to be the most effective and efficient strategy when working with children, especially those in the upper reaches of KS2 where the calculations can become unwieldy and cumbersome when the more traditional methods are used. Finally and perhaps the most significantly it marries the school’s desire to have a core strategy for each of the four rules of number and yet maintains a high level of creativity for the children to operate within. The following four examples are work undertaken by children at the top end of KS2. They are seeking to solve the calculation 48x28. Whilst they are all using the central strategy of the number line they are using a variety of methods to elucidate the final total. Eric’s Method Eric has multiplied by 10 and 10 to get 48 x 20. He has then multiplied 48x2 and used the answer of 96 as a total to use throughout so that he does not have so many multiplication steps to calculate. He will, however, have to add up the totals but he is hoping to double 96 and double the total again as a quicker mental method. Jane’s Method Jane has multiplied by 10 again but she has realised that she can double 48 and double it again easily in her head and has therefore gone for jumps of 48x4. 18 Dave’s Method Dave has decided that if he knows that 48x10=480 then to calculate 48x5 is relatively straightforward because it will simply be half of that total i.e. 240. This only leaves him 48x3 which he decides to take in two jumps; one of 48x2 and the other of 48x1 because he feels he can solve both of these mentally Georgina’s Method Georgina has noticed that 48x28 is only two 48’s away from 48x30. She can calculate the former mentally and then knows that she only needs to take 96 away from the total. Again she has appreciated that subtracting 96 is similar to taking away 100 and adding on four. Concluding Comments on the children’s Calculation Methods These calculations demonstrate that whilst there is a central core strategy being introduced to the children by the teacher, there remains much scope for the children to use their own mathematical understanding to solve the problem in hand. This keeps the teaching well within the “emergent” continuum and allows children to creatively explore solutions. One of the aspects of the number line that the children particularly commented on when they were asked to evaluate its effectiveness is that they felt they were in control of the numbers. If they got stuck calculating it one way there were always other options for them to turn to. They compared this with the more traditional column method/grid method where the partitioned numbers are set for you and allow for no flexibility. The key to this teaching approach is to focus the children’s minds carefully when choosing the jumps they wish to use. This is where the creativity is held and where the children can make the calculation a swift and effective process or conversely a nightmarish scenario of awkward and complex numbers. 19 Mathematical Understanding: Conceptual Developmental Framework The Conceptual Developmental Framework was designed to enable easy tracking of children through the learning process as well as an aid to the continuity and progression between classes at the end of each academic year. Mathematical Understanding: Conceptual Developmental Framework Calculation Progression Purpose of Strategy 2x3 CDF 1 3+3 Understanding CDF 2 2x3=6 See it CDF 3 2x3=6 Know it i.e. Rapid Recall CDF 4 12 lots of 3 Probably drawn out in an array Understanding CDF 5 4 x 3; 4 x 3; 4 x 3 or 2 x 6; 2 x 6 Understanding CDF 6 10 x 3 and 2 x 3 Effective and Efficient CDF 7 Written Number Line not column method Written/Consolidation With comprehension straight onto number line Written Method Consolidation or Calculation Straight onto Number Line Written Method Consolidation or Calculation 12 x 3 25 x 12 CDF 8 258 x 24 CDF 9 Notes for Teacher 1. The only place where we should need to model teaching is between CDF (Conceptual Developmental Framework) 5 and 6 where the children can be introduced to a more “efficient and effective” method of their own version if they don’t see it for themselves. All other stages should be scaffolded by the teacher in such a manner that the children learn through exploration. 2. CDF 1-5 and possibly 6 should have a heavy emphasis on the array as this is the most visually correct method of “showing” the calculation 3. The number line is introduced as a written method but has the advantage that it can be used as a calculation tool as well in later stages such as CDF 9. 4. The children should not be introduced to the number line until their concepts of multiplication and the use of “half partitioning” are in place, especially the half partitioning of tens and units. 20 How do I do a sum like 48 x 27? (Child’s Version) i. Can I do this in my head? ii. Estimate the answer iii. Take the sum and half partition the second number 4 8 x 2 7 iv. Draw the number line and decide what jumps you are going to take. Try to make jumps which will allow you to do all the calculations in your head. v. Next do the multiplication for all the parts. Remember wherever possible try to calculate all the parts “in your head” vi. Then calculate the final total by adding up all the parts you have multiplied. Again wherever possible try to do these calculations “in your head” where this is not possible then use pen and paper for some of them vii. Finally check your answer with your estimate and check it more accurately using a strategy such as “the inverse operation” 21 How do I break down a sum like 48 x 27? (Child’s Version) The children need to see that there are certain ways of breaking down the numbers into multiples that are more effective than others. For instance, whilst it is possible in the sum 48x27 to take the 48 and multiply it by 3 and 4 to get the 7 required in the units column this is by no means the most “efficient and effective” method. Children seem at a loss at times to choose the appropriate means to break down such a sum. The table below offers the most appropriate calculations to be used for any given number in the unit’s column. For some there is only one reasonable solution for others there are viable alternatives, but the children must come to see that those listed below are tried, tested and the most efficient ones to use. They should fall back on these as a natural default option, this is all part of the school’s overall strategy to streamline the methods used in calculation. Whilst the table illustrates how the numbers in the unit’s column may be broken down, the identical strategy should be adopted when using numbers in the tens, hundreds or thousands column. So if breaking down 7 into x5 and x2 is deemed “efficient and effective” then the same would apply to breaking down 70 when x50 and x20 would be used. Unit Number Effective and Efficient Operations Multiply by 1 Multiply by 1 Multiply by 2 Multiply by 2 Multiply by 3 Multiply by 1 and Multiply by 2. Total Multiply by 4 Multiply by 2 and Multiply by 2. Total Multiply by 5 Multiply by 10 and divide answer by 2 Multiply by 6 Multiply by 5 and Multiply by 1. Total Multiply by 7 Multiply by 5 and Multiply by 2. Total Multiply by 8 Multiply by 5, Multiply by 2, Multiply by 1.Total Multiply by 9 Multiply by 10 and multiply by 1. Subtract Multiply by 10 Multiply by 10 Double number, double and double again 22 The Number Line: The Wyche School Holistic Approach to Calculation (Multiplication) Stage 1: Multiplication on a Number Line Those teachers teaching younger children may wish to use the number line to illustrate concepts of multiplication. Whilst we would all recognise that the array is a far more powerful visual tool, the use of the number line in this way will give children a sense of continuity rather than seeing a number line for multiplication for the first time later on. It also allows the school’s format and layout to be rehearsed. It is crucial that the children are able to calculate these mentally and that the number line is not seen as a calculation tool at this stage. Stage 1 4x2=8 12 x 4 = 48 Stage 2: Number Line (TU x U) The number line can also be used to calculate in the following manner where a TU number is followed by a U. This is because whilst the 12 is being partitioned the 4 is being used holistically as a whole number. Stage 2 12 x 4 = 48 Stage 3: Number Line (TUxTU) The Number line should never be used where both numbers to be multiplied are partitioned. In this instance the grid method is far more appropriate and if used in this way it will only serve to confuse children when they are asked to use the numbers holistically. In this sense this is a single track method that is only to be used when one number is partitioned. In the example illustrated the 27 is kept as a whole number and multiplied by the 10 and the 2 respectively. Stage 3 27 x 12 Stage 4: Number Line (HTUxTU) The children must be encouraged to see that the power of this method is that they are in control of the sum not the numbers. In the grid method the calculations are determined by the numbers in the sum. Here the children have the freedom to choose the calculations they feel are easiest. This is important to stress. There are no right or wrong methods only those that are more “efficient or effective”. If children end up using small jumps to make the sum easier then one must conclude that the calculation itself is probably at a level beyond them and the teacher should redress the level of differentiation offered to that child. Stage 4 48 x 27 Given freedom to tackle this sum one child might break down the calculations in to a series of 10’s and then multiply by 5 and 2. However another child may find the 5 calculation a little complex and prefer to multiply by 10 and a series of 2’s with a single number to finish. 23 Stage 5: Number Line (HTU x HTU) The children need to see that using 100’s and 10’s in multiplying the numbers is a means of quickly knocking the sum down to a manageable size. The key factors remain that they see themselves as controlling the calculations and that there are no right or wrong answers in terms of method Stage 5 48 x 256 = 12288 24 Progression on to Formal Written Methods The school has made a policy decision that the formal column method for multiplication will not be taught until Year 6. The rationale for this is held in the fact that the school believes that to move children on to the written method prematurely reduces the opportunity for true mathematical understanding and creates pockets of misunderstanding that teachers will later have to backfill. This is mainly due to the abstract nature of the calculation where a “full partitioning” of the numbers reduces them to a series of unit measures. Therefore the school will only present the formal written calculations to children for whom there is a wealth of understanding with regard to the whole concept of multiplication; and for whom the column method might present a more effective and efficient solution for specific calculations. In this sense it will simply become another tool in the child’s armoury of calculation strategies. Multiplication: Progression of Written Methods (These methods to be taught in Year 6 only) The following stages lean heavily on the material from the Renewed Framework document on Calculation. The criteria for using these written methods are that the children are secure in their mental strategies for the calculations they are set. The key question for children to ask remains the same “Can I do this in my head?” Indeed many of the strategies rely on the use of mental calculation embedded within them. For instance, the grid method (TUxTU) relies on children being able to mentally add the calculations in the rows of the grid. Stage 1: Mental multiplication using partitioning Mental methods for multiplying TU × U can be based on the distributive law of multiplication over addition. This allows the tens and ones to be multiplied separately to form partial products. These are then added to find the total product. Either the tens or the ones can be multiplied first but it is more common to start with the tens. Stage 1 Informal recording in Year 4 might be: Also record mental multiplication using partitioning: 14 3 (10 4) 3 (10 3) (4 3) 30 12 42 43 6 (40 3) 6 (40 6) (3 6) 240 18 258 Note: These methods are based on the distributive law. Children should be introduced to the principle of this law (not its name) in Years 2 and 3, for example when they use their knowledge of the 2, 5 and 10 times-tables to work out multiples of 7: 7 3 (5 2) 3 (5 3) (2 3) 15 6 21 Stage 2: The grid method This is based on the distributive law and links directly to the mental method. It is an alternative way of recording the same steps. It is better to place the number with the most digits in the left-hand column of the grid so that it is easier to add the partial products. Stage 2 38 × 7 = (30 × 7) + (8 × 7) = 210 + 56 = 266 25 Stage 3: Grid Method in columns The next step is to move the number being multiplied (38 in the example shown) to an extra row at the top. Presenting the grid this way helps children to set out the addition of the partial products 210 and 56. Stage 3 38 x 7 Stage 4: Expanded short multiplication • The next step is to represent the method of recording in a column format, but showing the working. Draw attention to the links with the grid method above. • Children should describe what they do by referring to the actual values of the digits in the columns. For example, the first step in 38 × 7 is ‘thirty multiplied by seven’, not ‘three times seven’, although the relationship 3 × 7 should be stressed. Stage 4 38 x 7 = 266 Stage 5: Short multiplication Stage 5 38 7 266 • The recording is reduced further, with carry digits recorded below the line. • If, after practice, children cannot use the compact method without making errors, they should return to the expanded format of stage 3. 30 8 7 210 56 266 30 7 210 8 7 56 38 7 210 56 266 5 The step here involves adding 210 and 50 mentally with only the 5 in the 50 recorded. This highlights the need for children to be able to add a multiple of 10 to a twodigit or three-digit number mentally before they reach this stage. Stage 6: Two-digit by two-digit products • Extend to TU × TU, asking children to estimate first. • Start with the grid method. The partial products in each row are added, and then the two sums at the end of each row are added to find the total product. • As in the grid method for TU × U in stage 4, the first column can become an extra top row as a stepping stone to the method below. Stage 6 56 × 27 is approximately 60 × 30 = 1800. Stage 7: Introduction to the Columns (TU) Stage 7 56 × 27 is approximately 60 × 30 = 1800. 56 27 1000 50 20 1000 120 6 20 120 350 50 7 350 42 6 7 42 1512 • Reduce the recording, showing the links to the grid method above. 1 26 Stage 8: Traditional Column Method • Reduce the recording further. • The carry digits in the partial products of 56 × 20 = 120 and 56 × 7 = 392 are usually carried mentally. Stage 8 56 × 27 is approximately 60 × 30 = 1800. 56 27 1120 56 20 392 56 7 1512 1 Stage 9: Three-digit by two-digit products • Extend to HTU × TU asking children to estimate first. Start with the grid method. • It is better to place the number with the most digits in the left-hand column of the grid so that it is easier to add the partial products. Stage 9 286 × 29 is approximately 300 × 30 = 9000. Stage 10: Expanded Columns (HTU) • Reduce the recording, showing the links to the grid method above. • This expanded method is cumbersome, with six multiplications and a lengthy addition of numbers with different numbers of digits to be carried out. There is plenty of incentive to move on to a more efficient method. Stage 10 286 29 4000 200 20 4000 1600 80 20 1600 120 6 20 120 1800 200 9 1800 720 80 9 720 54 6 9 54 8294 1 Stage 11: Traditional Column Method (HTU) • Children who are already secure with multiplication for TU × U and TU × TU should have little difficulty in using the same method for HTU × TU • Teachers must discern whether this is because the children are following the “trick” of using numbers as digits (which in essence there in no problem with) as long as they have the corresponding understanding of the calculation as whole numbers. • Again, the carry digits in the partial products are usually carried mentally. Stage 11 286 × 29 is approximately 300 × 30 = 9000. 286 29 5720 286 20 2574 286 9 8294 1 27 Division: Progression within Written and Mental Methods Division remains in children’s minds the most conceptually difficult of the four rules to comprehend. This is a national as well as a local issue as “difficulties with fully understanding division persist into secondary school” (Hart, 1981). It has become apparent from our early tracking of children in KS2 that the issues with division far outweigh those in addition, multiplication and subtraction. As one child said “It is because in division you have two things to concentrate on; taking away and your times tables” (Olivia) There is probably much truth in this observation. On top of that the division calculation involves a greater abstraction of numbers. 32x12 offers two sums that can be readily seen as 32x10 and 32x2. However whilst 84÷7 can be calculated as 7x10 and 2x7 these calculations are “hidden” from the children as they are not explicit within the numbers used in the original calculation. Therefore the children must “see” them and “create” them for themselves. In this sense the calculation for division is potentially more abstract than for multiplication. Also whilst in multiplication it is possible for children to enter a transition phase of “Full Partitioning” on their path to calculating with TU this is not possible in division. As we saw above, the calculation 32x12 provides the opportunity for children to calculate as follows; 32x10 and 32x2, however solving 384÷12 using “Full Partitioning” is not possible. The child who calculates 384÷10=38.4 and 384÷2=192 finds the resultant total is 230.4. Hopefully even a limited understanding of calculation should allow the child to discern that the answer is far from correct. This reveals a basic lack of understanding as to the process that occurs physically in the operation of division. This then leads children to lean heavily on prior knowledge of taught learning strategies from the other four rules, these are often found sadly wanting when there is no understanding of what is happening within the calculation. This has important ramifications for the teaching process as it means teachers will not be able to move through “Full Partitioning” as a staging post, en-route to the more efficient and effective “Half Partitioning” method. Similarly the concept of the remainder also adds a further complication as it is hidden in the calculation until the end, where an additional calculation step is required (often addition and/or subtraction) before being able to attain the answer. There are no such additional steps within multiplication, which is based around the much more straightforward idea of “What you see is what you get.” In this sense it is not surprising that division remains an Achilles heel for most children. Therefore there should be a great emphasis placed upon the preparatory work of conceptual understanding before the child moves on to any written calculating strategies. 28 Division: Whole School Approach In Key stage 1, the children are introduced to the concept of division through the notion of “sharing”. This is the foundation for all understanding and is less abstract compared with its “grouping” counterpart. The reason being that in sharing 12÷4 the child can see how many objects are to be shared and how many people they are to be shared with. The quotient being how many each person has in the end. However the approach the school has adopted at present involves the children having a firm understanding of the concept of grouping. This is more abstract for whilst the initial number of objects to be shared is known the number of people to be shared with remains an unknown. This method relies on the principles of division being seen as a series of repeated subtractions based on the divisor. So 12÷4 becomes 12 -4 -4 -4 the answer being 3 because it took 3 lots of 4 to get back to zero from 12. For grouping the key question therefore is “How many 4’s are there in 12?” rather than “I have 12 how many will 4 people get?” It is important that children have a clear path set for them as they make the transition between one concept of division to the other. In recent lessons the children have been taught the difference between the two and shown clearly that there are two methods by which the quotient can be calculated. This is important because the number line method teaches division in relation to its multiplication counterpart. The key strategy for the calculation 324÷14 will be to answer the question “How many 14’s are there in 324?” and children will be encouraged to calculate this mentally using the number line as a support framework. In one sense this is the identical strategy to multiplication, except that they will be starting the number line on the right and subtracting the calculated totals; thereby seeking to underscore the relationship between division and repeated subtraction. It is important that the children “see” division as a pure mathematical concept, rather than using their knowledge of multiplication as a means to bypass their true understanding of the process of division. Having said that, the school recognises that this approach does not offer a full replication of the division process for whilst the method readily replicates the concept of grouping it is not cognitively secure with regard to sharing. “Division comes in two conceptual frameworks namely sharing and grouping. Whilst the former is well understood by primary children the latter is not.” (Nunes and Bryant,1996). In that sense it is a pragmatic approach which offers children a strategy of calculation, however the school recognises that this approach does not provide a framework for secure understanding of the concepts behind it. This must be done elsewhere. The role of concrete materials in the teaching of division will be a key to successful learning. We have tended to move away from cubes and Dienes material, especially in the upper reaches of Key Stage 2 but the abstract nature of the subject matter means that there should be much underpinning of the concepts with as great a variety of practical materials as is possible. The child’s ability to “see” and visualise 10 groups of 24 will greatly enhance their ability to calculate effectively when this is transferred to the more abstract number line. 29 I am rapidly coming to the conclusion that the best way to develop a secure cognitive understanding is actually through the use of practical, real-life topic based maths (as advocated by the renewed framework). It is only when children experience Maths in real contexts that they can truly understand what 14 divided by 3 really means, with its groups of 3 and its 2 left over. These are concepts we should not “teach” in a traditional lesson based environment, as they are too abstract for children to appreciate the nuances of what is happening to the numbers. For instance, if you were to ask two pre-school children to share 3 sweets between them despite the apparent conceptual complexity you soon appreciate they have an intricate working of both division and remainders! The school is in a good position to deliver this through its desire to reinvent a more “real-life” based curriculum and the central strand of number-line calculation should therefore be underpinned by work of a practical nature. Related to this is the oft-quoted fact running throughout this document that, in the past we have moved children onto calculation too quickly before understanding is fully in place. We should see the acquisition of these skills in a whole school context. To this end the curriculum process of calculation acquisition should be tackled as a long distance race not a sprint. Those who start too fast often burn out before the end. Whilst we would want to challenge children in every year group we should resist the pressure (especially in the early years of KS2) to rush into calculation strategies when the children would probably benefit in the longer term from further work on developing their understanding of division. Whole School Approach: Standardisation of setting out a calculation The school has adopted the above approach for setting out division on a number line. Using 1344 ÷ 48 as an illustration the children should undertake the following: i. The jumps should outline the “groups of 48” that the children have chosen. The calculation is written inside the jump i.e. 10 x 48 (10 lots of 48). It should be written as 10 x 48, not 48 x 10 to consolidate the fact that this is 10 groups of 48 ii. The number to be subtracted should be placed underneath the jump. This is so that the child is quite clear on what they are subtracting. iii. The number of groups is also placed above the jump. This is so that at the end of the calculation the children can see clearly how many groups of 48 it has taken to get to zero. In this instance the answer would be 10 + 10 + 4 + 4. 30 Progression in Upper Key Stage 2 Increasingly within the upper reaches of Key Stage 2 the children should be encouraged to use a range of mental strategies to support their work on the number line. In the example above it is hoped that most children working at this level will “know” that 48x2=96 and that therefore the two jumps of 10 are superfluous and that one jump of 20 would suffice. Similarly if they can calculate that 48x4 is 192 they should be able to double that total mentally through a strategy such as 200+200-16. Thereby creating a number line that looks more like that below: Increasingly it is hoped that children will be calculating mentally and using the number line purely as a visual support. In the latter stages of Year 6 it has been noted that the children dispense with the number line yet still using the principles of half partitioning are calculating answers mentally alongside informal jottings. So that the above calculation is reduced to 48x20=960 and 48x8= 48x2x2x2 = 96; 192; 384. Therefore the answer is 960+384 This too they should be able to add mentally, or quickly resort to a column addition sum. 31 The Number Line: The Wyche School Holistic Approach to Calculation (Division) Introduction: Division on a Number Line Those teachers teaching younger children may wish to use the number line to illustrate concepts of division. Whilst we would all recognise that there are more powerful tools, the use of the number line in this way will give children a sense of continuity rather than seeing a number line for division for the first time later in the school. It also allows the school’s format and layout to be rehearsed. It is crucial that the children are able to calculate these mentally and that the number line is not seen as a calculation tool at this stage. Introduction 8÷4=2 Stage 1: Division of TU÷ U using numbers within the times table Stage 1 The use of the number line for large multiples needs to be used judiciously. Whilst it may consolidate the concept of repeated subtraction it is not the most powerful tool either visually, kinaesthetically or conceptually to illustrate division. It may well be argued that children at this stage in their development should be making greater use of concrete materials and real life situation to flesh out their basic understanding. 27 ÷ 3 = 9 Stage 2: Partitioning using the number line TU ÷ U Stage 2 Where the children have a clear understanding that the original number is being shared into groups of the divisor then they can be encouraged to use multiples of factors to allow for ease of calculation. It should be borne in mind that this is a major cognitive and abstract step and should not be undertaken without a secure understanding of the grouping principle. 48 ÷ 4 = 12 32 Stage 3: Division HTU ÷ U At this stage in their development the children should have a thorough understanding that what they are seeking to achieve through the sum 224 ÷ 8 is to find out how many 8’s there in 224. The process could involve “counting up” to 224 and although in essence this is probably what the children will be doing cognitively, the presentation on the number line is one of “repeated subtraction” in the sense that the numbers are taken away from 224 and reduced to zero. The key is to get the children to see that they can “easily lose” groups of 8 by multiplying by 10. This should allow them to get quickly into an arena where they can use their knowledge of times tables to assist the final calculation i.e. 64÷8. Stage 3 Stage 4: Division HTU ÷ U with remainder The number line provides a clear opportunity for children to understand the concept of the remainder, as the number that remains when the total has been sorted into equal groups. Stage 4 It will also enable a rich discussion when children are dividing a number where they (for ease of calculation) take the number into negative numbers and then seek to calculate the remainder. In the second example (see right) the children will often assume that the remainder is 6. 224 ÷ 8 228 ÷ 8 234 ÷ 8 Stage 5: Division HTU ÷ TU The principle here is the same as previous; namely that the children should find creative ways of “grouping” the numbers so as to reduce the total down to a place where they can readily access the final answer through their knowledge of times tables. Stage 5 336 ÷ 14 Stage 6: Division ThHTU ÷ TU As we move into the larger numbers the opportunities for a wide range of strategies to solve a given calculation come to the fore. As with multiplication this allows the children to develop a range of mental strategies that the number line can support and thus marry the need to establish a single default strategy alongside an enriched creative maths curriculum. Stage 6 1344 ÷ 48 33 Division: Progression of Written Methods (These methods to be taught in Year 6 only) The following stages lean heavily on the material from the Renewed Framework document on Calculation. The criteria for using these written methods are that the children are secure in their mental strategies for the calculations they are set. There is a definite linear progression in the teaching of division and security of knowledge and understanding of each stage must precede the teaching of the next. The key question remains the same “Can I do this in my head?” Indeed many of the strategies rely on the use of mental calculation embedded within them. As stated elsewhere the children should not be moved on to the written method prematurely as it reduces the opportunity for true mathematical understanding and creates pockets of misunderstanding that teachers will later have to backfill. Stage 1: Mental division using partitioning Stage 1 • Mental methods for dividing TU ÷ U can be based on partitioning and on the distributive law of division over addition. This allows a multiple of the divisor and the remaining number to be divided separately. The results are then added to find the total quotient. • Many children can partition and multiply with confidence. But this is not the case for division. One reason for this may be that mental methods of division, stressing the correspondence to mental methods of multiplication, have not in the past been given enough attention. • Children should also be able to find a remainder mentally, for example the remainder when 34 is divided by 6. One way to work out TU ÷ U mentally is to partition TU into a multiple of the divisor plus the remaining ones, then divide each part separately. Stage 2: Mental Division using the grid Stage 2 Using the grid method to make links with multiplication as well as reinforcing the mental approaches with questions such as ‘How many sevens in seventy?’ and: ‘How many sevens in fourteen?’ Another way to record is in a grid, with links to the grid method of multiplication. Informal recording in Year 4 for 84 ÷ 7 might be: In this example, using knowledge of multiples, the 84 is partitioned into 70 (the highest multiple of 7 that is also a multiple of 10 and less than 84) plus 14 and then each part is divided separately using the distributive law. As the mental method is recorded, ask: ‘How many sevens in seventy?’ and: ‘How many sevens in fourteen?’ Stage 3: Mental Division with expanded recording (including remainders) This approach simply allows for a numerical recording of the stages the children go through in the partitioning process. Stage 3: Mental Division with expanded recording Also record mental division using partitioning: 64 ÷ 4 = (40 + 24) ÷ 4 = (40 ÷ 4) + (24 ÷ 4) = 10 + 6 = 16 87 ÷ 3 = (60 + 27) ÷ 3 = (60 ÷ 3) + (27 ÷ 3) = 20 + 9 = 29 34 Stage 4: Mental Division with expanded recording (including remainders) This stage includes the use of remainders Stage 4: Mental Division with expanded recording (including remainders) Remainders after division can be recorded similarly. 96 ÷ 7 = (70 + 26) ÷ 7 = (70 ÷ 7) + (26 ÷ 7) = 10 + 3 R 5 = 13 R 5 Stage 5: Short division of TU ÷ U Stage 5 • ‘Short’ division of TU ÷ U can be introduced as a more compact recording of the mental method of partitioning. • Short division of a two-digit number can be introduced to children who are confident with multiplication and division facts and with subtracting multiples of 10 mentally, and whose understanding of partitioning and place value is sound. • The accompanying patter is ‘How many threes divide into 80 so that the answer is a multiple of 10?’ This gives 20 threes or 60, with 20 remaining. We now ask: ‘What is 21divided by three?’ which gives the answer 7. For 81 ÷ 3, the dividend of 81 is split into 60, the highest multiple of 3 that is also a multiple 10 and less than 81, to give 60 + 21. Each number is then divided by 3. 81 ÷ 3 = (60 + 21) ÷ 3 = (60 ÷ 3) + (21 ÷ 3) = 20 + 7 = 27 The short division method is recorded like this: 20 7 3 60 21 This is then shortened to: 27 3 8 21 The carry digit ‘2’ represents the 2 tens that have been exchanged for 20 ones. In the first recording above it is written in front of the 1 to show that 21 is to be divided by 3. In second it is written as a superscript. The 27 written above the line represents the answer: 20 + 7, or 2 tens and 7 ones. Stage 6: ‘Expanded’ method for HTU ÷ U • This method is based on subtracting multiples of the divisor from the number to be divided, the dividend. • For TU ÷ U there is a link to the mental method. • As you record the division, ask: ‘How many nines in 90?’ or ‘What is 90 divided by 9?’ • Once they understand and can apply the method, children should be able to move on from TU ÷ U to HTU ÷ U quite quickly as the principles are the same. • This method, often referred to as ‘chunking’, is based on subtracting multiples of the divisor, or ‘chunks’. Initially children subtract several chunks, but with practice they should look for the biggest multiples that they can find to subtract. • Chunking is useful for reminding children of the link between division and repeated subtraction. Stage 6 97 ÷ 9 9 97 90 9 10 7 Answer: 10 R 7 6 196 60 6 10 136 60 6 10 76 60 6 10 16 12 6 2 4 32 Answer: 32 R 4 35 • However, children need to recognise that chunking is inefficient if too many subtractions have to be carried out. Encourage them to reduce the number of steps and move them on quickly to finding the largest possible multiples. Stage 7: Shortened Chunking Method and Estimation Stage 7: Shortened Chunking Method and Estimation • The key to the efficiency of chunking lies in the estimate that is made before the chunking starts. Estimating for HTU ÷ U involves multiplying the divisor by multiples of 10 to find the two multiples that ‘trap’ the HTU dividend. • Estimating has two purposes when doing a division: – to help to choose a starting point for the division; – to check the answer after the calculation. • Children who have a secure knowledge of multiplication facts and place value should be able to move on quickly to the more efficient recording on the right. To find 196 ÷ 6, we start by multiplying 6 by 10, 20, 30, … to find that 6 × 30 = 180 and 6 × 40 = 240. The multiples of 180 and 240 trap the number 196. This tells us that the answer to 196 ÷ 6 is between 30 and 40. Start the division by first subtracting 180, leaving 16, and then subtracting the largest possible multiple of 6, which is 12, leaving 4. Stage 8: Short division of HTU ÷ U Stage 8 • ‘Short’ division of HTU ÷ U can be introduced as an alternative, more compact recording. No chunking is involved since the links are to partitioning, not repeated subtraction. • The accompanying patter is ‘How many threes in 290?’ (the answer must be a multiple of 10). This gives 90 threes or 270, with 20 remaining. We now ask: ’How many threes in 21?’ which has the answer 7. • Short division of a three-digit number can be introduced to children who are confident with multiplication and division facts and with subtracting multiples of 10 mentally, and whose understanding of partitioning and place value is sound. 6 196 180 6 30 16 12 6 2 4 32 Answer: 32 R 4 The quotient 32 (with a remainder of 4) lies between 30 and 40, as predicted. For 291 ÷ 3, because 3 × 90 = 270 and 3 × 100 = 300, we use 270 and split the dividend of 291 into 270 + 21. Each part is then divided by 3. 291 ÷ 3 = (270 + 21) ÷ 3 = (270 ÷ 3) + (21 ÷ 3) = 90 + 7 = 97 The short division method is recorded like this: 90 7 3 290 1 3 270 21 This is then shortened to: 97 3 2 9 21 The carry digit ‘2’ represents the 2 tens that have been exchanged for 20 ones. In the first recording above it is written in front of the 1 to show that a total of 21 ones are to be divided by 3. The 97 written above the line represents the answer: 90 + 7, or 9 tens and 7 ones. 36 Stage 9: Long division The next step is to tackle HTU ÷ TU. Stage 9 How many packs of 24 can we make from 560 biscuits? The layout on the right, which links to chunking, is in essence the ‘long division’ method. Recording the build-up to the quotient on the left of the calculation keeps the links with ‘chunking’ and reduces the errors that tend to occur with the positioning of the first digit of the quotient. Start by multiplying 24 by multiples of 10 to get an estimate. As 24 × 20 = 480 and 24 × 30 = 720, we know the answer lies between 20 and 30 packs. We start by subtracting 480 from 560. Conventionally the 20, or 2 tens, and the 3 ones forming the answer are recorded above the line, as in the second recording. In effect, the recording above is the long division method, though conventionally the digits of the answer are recorded above the line as shown below. 23 24 560 480 80 72 8 Answer: 23 R 8 24 560 20 480 24 20 80 3 72 24 3 8 Answer: 23 R 8 37 The following are an illustrative summary of the sequencing approaches to be used for the four rules. For brevity they are illustrated by strategies that might be taught to children in the middle of Key Stage 2. The full progression is outlined in the document “Calculation: School Version” Addition The first number in the addition sentence is kept as a 3 digit figure and only the second numeral is partitioned into its constituent parts of 200, 20 and 6. The focus is on the place value of each digit remaining intact so 200 is seen as such not a 2 in the hundreds column. Calculation Exemplar Subtraction As with addition counterpart the first numeral maintains its sense of totality as a single figure whilst the second number is partitioned into its place valued digits. The children will choose a simple counting back or a bridging strategy where the answer needs bridging through a multiple of 10 Calculation Exemplar Multiplication The first number remains intact whilst the child creates a series of “sequenced jumps” to attain the answer. These jumps should be as logical as possible e.g. For x26 two jumps of 10, a jump of 5 and a jump of 1 provides a judicious and efficient strategy Calculation Exemplar Division The key strategy will be to answer the question “how many 14’s are there in 324?” in seeking to solve the calculation 324÷14. Children will be encouraged to calculate this mentally using the number line as a support framework. In one sense this is the identical strategy to multiplication, except that they will be starting the number line on the right and subtracting the calculated totals; thereby seeking to underscore the relationship between division and repeated subtraction. Calculation Exemplar 256 + 226 74 - 27 27 x 12 48 ÷ 4 38