MULTIPLICATION Mental strategies for multiplication include counting on in steps of a constant size, doubling, using commutativity and multiplying by partitioning a number, multiplying each part and then putting it back together again, e.g. double 34 by doubling 30 and doubling 4. The ‘grid’ written method builds on this partitioning of numbers, performing the multiplication on each part and then adding the result. These notes show the stages in building up to using an efficient method for twodigit by one-digit multiplication by the end of Year 4, two-digit by two-digit multiplication by the end of Year 5, and three-digit by two-digit multiplication by the end of Year 6. To multiply successfully, children need to be able to: count on in steps, e.g. work out 10 × 3 by counting on in 10s understand commutativity, e.g. work out 5 × 7 by recalling seven 5s if they don’t yet know their seven times table recall all multiplication facts to 10 × 10 by the end of Year 4 partition number into multiples of one hundred, ten and one; work out products such as 70 × 5, 70 × 50, 700 × 5 or 700 × 50 using the related fact 7 × 5 and their knowledge of place value; add multiples of 10 (such as 60 + 70) or of 100 (such as 600 + 700) using the related addition fact, 6 + 7, and their knowledge of place value; add combinations of whole numbers. 1 Calculation policy September 2011 Foundation Stage Children will experience equal groups of objects. They will count in 2s and 10s and begin to count in 5s. They will work on practical problem solving activities involving equal sets or groups. Year 1 Double single-digit numbers Double 5 Count on in steps 1 2 3 4 5 6 2, 4, 6, 8, 10… 2, 4, 6, Double 6, two groups of 6 10 10, + 20, 10 8 8, + 30, 2 Calculation policy 7 September 2011 9 10… 10 40, 50… 10 Year 2 Count on in repeated steps Find five 3s, six 5s, five 10s Use commutativity Know that 5 × 3 can be worked out as three 5s or five 3s 3×5 = 5×3 Double two-digit numbers Double 23 is double 20 plus double 3, 40 + 6 = 46 3 Calculation policy September 2011 Year 3 Multiply single-digit numbers together using counting on and known multiplication facts 8 × 6: count up in 8s or 6s, or double 4 × 6 3 X 6 0 6 12 Use mental strategies 26 × 4: double 26 and double again 14 × 20: double 14 and multiply by 10 24 × 5: multiply by 10 and halve 13 × 9: 13 × 10, then subtract 13 13 × 11: 13 × 10, then add 13 18 Double two-digit numbers -Double 46 46 80 Year 4 Multiply two-digit numbers by singledigit numbers using the grid method 93 x 8 = 744 12 92 Multiply teens numbers by single-digit numbers 17 × 3 10 × 3 = 30; 7 × 3 = 21 30 + 21 = 51 x 90 3 8 720 24 4 Calculation policy September 2011 =744 Year 5 Year 6 Continue to use mental strategies Double 256: double 250 plus double 6 35 × 14: double 35, halve 14, 70 × 7 = 490 36 × 50: multiply by 100, then halve 360 13 × 19/21: multiply by 20, +/- 13 Continue to use mental strategies 14 × 15: 14 × 10, halve the result and then add the two parts together, 140 + 70 = 210 39 × 25: multiply by 100, then divide by 4 13 × 49/51: multiply by 50, +/- 13 8.6 × 7: (8 × 7) + (0.6 × 7) = 56 + 4.2 = 60.2 Multiply three-digit numbers by singledigit numbers and two-digit numbers two-digit numbers 256 x 3 = 768 x 200 50 6 3 600 150 18 Multiply four-digit numbers by singledigit numbers and three-digit numbers two-digit numbers 4256 × 6 = 3936 =768 x 4000 200 50 6 6 2400 1200 300 36 =3936 26 x 32 = 832 256 x 23 = 5888 x 20 6 30 600 180 2 40 12 600 180 40 12 832 x 200 20 4000 3 600 50 6 1000 120 150 18 180 5 Calculation policy September 2011 4000 1000 120 600 150 18 5888 DIVISION Children consider division as sharing (halving and quartering) and division as grouping (how many groups in…?). The written method used for division is based on the ‘grouping’ method of division and is known as ‘chunking’. These notes show the stages in building up to using an efficient method for twodigit by one-digit division by the end of Year 4, three-digit by one-digit division by the end of Year 5, and three-digit by two-digit division by the end of Year 6. To divide successfully, children need to be able to: count on in steps, e.g. work out 18 ÷ 3 by counting on in 3s understand and use multiplication and division as inverse operations; partition two-digit and three-digit numbers in different ways, e.g. partition 42 into 30 and 12 when dividing by 3 (dividing 30 by 3 and 12 by 3); recall multiplication and division facts to 10 × 10, recognise multiples of one-digit numbers and multiply multiples of 10 or 100 by a single-digit number using their knowledge of multiplication facts and place value; understand that division can leave a remainder; understand that division by grouping and sharing (halving/quartering) give the same answer and choose which is most efficient for a given calculation use multiplication facts and place value to estimate how many times one number divides into another – for example, how many sixes there are in 147, or how many 23s there are in 472; subtract numbers to find how much still needs to be divided when using chunking. 6 Calculation policy September 2011 Foundation Stage Children will understand equal groups and share items out in play and problem solving. They will count in 2s and 10s and later in 5s. Year 1 Halving by Sharing Find half of 8, by sharing 8 cubes between two people or folding a strip of 8 objects in half. Begin to find a quarter by halving and halving again, e.g. find a quarter of 8. 7 Calculation policy September 2011 Year 2 Halving and quartering Find half and a quarter of 20. Grouping 18 ÷ 3, how many groups of 3 are in 18? 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 188 Use multiplication facts to help, e.g. 60 ÷ 10: how many 10s are in 60? 20 ÷ 5: how many 5s are in 20? Realise that division can sometimes leave some ’left over’ 16 ÷ 3 Year 3 Year 4 Grouping Using multiplication facts: 35 ÷ 5 = 7 because I know there are seven 5s in 35. Chunking Taking off a chunk of the divisor using a multiple of 10: 67 ÷ 3, 100 ÷ 6 r4 Finding remainders 38 ÷ 5. Seven 5s make 35, leaving 3 left over. X 7 100 6 r3 100 - 60 10 x 6 6 x 6 40 Dividing giving answers just over 10 42 ÷ 3: x10 x4 - 36 4 16 100 ÷ 6 = 16 remainder 4 8 Calculation policy September 2011 Year 5 Year 6 Chunking Taking off larger chunks using estimation, multiplication facts and place value: 196 ÷ 6 X30 x2 r4 Chunking Using knowledge of multiplication facts and place value to use chunking efficiently to divide three-digit numbers by singledigit and begin to divide by two-digit numbers: 556 ÷ 25 X20 x2 r6 6 × 10 = 60 6 × 20 = 120 6 × 30 = 180 6 × 40 = 240 The answer is between 30 and 40, so I’ll subtract 30 lots of 6, leaving 16. 25 × 10 = 250 25 × 20 = 500 The answer is between 20 and 30, so I’ll subtract 20 lots of 25, leaving 56. 196 6 196 - 180 30 x 556 6 556 16 - 12 25 2 x - 6 500 20 x 25 2 x 25 56 4 - 32 50 6 196 6 = 32 r 4 22 556 25 = 22 remainder 6 9 Calculation policy September 2011