Year 6 Teaching Sequence summer 9 – Multiplication and division (five days) Prerequisites: Know by heart all multiplication and division facts for the 2 to 10 times tables Double quickly any two-digit number e.g. 78, 7.8. 0.78, and derive the corresponding halves (see oral and mental starter bank 9) Double multiples of 10 to 1000 e.g. double 360, and derive the corresponding halves (see oral and mental starter bank 9) Use knowledge of place value and multiplication facts to work out multiplication and division involving decimals (e.g. 0.8 × 7, 4.8 ÷ 6) (see spring teaching sequence 3) Multiply two-digit numbers by single-digit numbers by partitioning, e.g. 4.7 × 6 = (4 × 6) + (0.7 × 6) (see spring teaching sequence 3) Approximate first when multiplying and dividing (see spring teaching sequence 4 and summer oral and mental starter bank 9) Use the grid method to multiply three-digit numbers by two-digit numbers including those with one decimal place (see spring teaching sequence 4) Overview of progression: Children use known multiplication facts to derive others, e.g. doubling the 8 times table to get the 16 times table or adding the 10 and 7 times table to give the 17 times table. They use the strategy of halving and doubling to multiply even numbers by multiples of five, e.g. 48 × 35. The grid method of multiplication is used to multiply three-digit numbers with two decimal places by single-digit numbers, estimation is encouraged. Children begin to divide by decimal numbers, e.g. 35 ÷ 2.5, by doubling the divisor and doubling the answer. Quotients are expressed as vulgar and decimal fractions e.g. 23 ÷ 4 = 5 ¾, or 5.75. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS9 – Sum – 5days Note that lots of the sessions in this sequence involve lots of playing with numbers, halving and doubling and using known facts to derive new ones. This should improve children’s flexibility and confidence with multiplication, division and place value and this is perhaps more important than whether they remember the strategies which emerge or not. Note that the decimal point is not taken out of calculations and then replaced at the end as children can be confused about where to put it. Instead the place value of each digit is maintained throughout the calculation. Watch out for children who make place value errors when multiplying by numbers with two decimal places. Encourage them to estimate as their estimate can help them to realise that an answers is wrong. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS9 – Sum – 5days Objectives: Use factors to multiply e.g. multiply by 8 by multiplying by 4 then doubling Use number facts to generate new multiplication facts, e.g. develop the 24× table by multiplying the 6× table by 4 Develop the 17× table by adding the 10 and 7× tables Multiply by halving one number and doubling the other, e.g. calculate 35 × 16, by calculating 70 × 8 Approximate first Use the grid method to multiply three-digit numbers by single-digit numbers including two decimal places, e.g. 4.92 × 3 Give an answer to division as a vulgar fraction, e.g. 90 ÷ 7 = 12 6/7 Give an answer to division as a decimal fraction, e.g. 61 ÷ 4 = 15.25 Use written methods to divide numbers including decimals Explain methods and reasoning orally Whole class Group activities Paired/indiv practice Today we’re going to learn our 16 times table! Launch the ITP Number dials and choose multiples of 8. Use to recite multiplication facts for the eight times table clicking on the multiples to reveal them each time. How could we use this times table to find multiplication facts for the 16 times table? Agree that you could double each number. Recite the 16 times table slowly pointing to the corresponding multiples of eight as you do so. How could we find the 24 times table? Draw out that they could double multiples of 12 if they know them, triple multiples of 8, or quadruple multiples of 4. Which way would you prefer? Use the times table chosen by the majority, write it as list of vertical multiplications on the board, and next to it work together to write the 24 times table. Do you think we will have an odd number in this times table? Why not? Group of 4-5 children How could we find the 15 times table? Discuss how they could triple the 5 times table, but they could also add numbers in the 10 and 5 times tables. Ask chn to choose their preferred way to find the 15 times table. How could we find the 17 times table? Ask chn to work in pairs to write the multiplication facts for the 17 times table. How many odd numbers do you think you will have? Why? Harder: Chn choose a way to derive the 19 times table and the 21 times table. Chn work in pairs to derive the 14 times table, the 18 times table and a times table of their own choice. Easier: Chn derive the 12 times table and the 30 times table. Harder: Chn derive the 32 times table, the 3.5 times table and a times table of their own choice. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Resources ITP Number dials Y6 Maths TS9 – Sum – 5days Write 35 × 16 on the board. We could work this out by finding 10 lots of 35 and 6 lots of 35, and then adding the two products together. But there is a special way of multiplying multiples of 5 by even numbers such as 16 which can be quite useful. If we multiplied 35 by 8 instead of 16, what could you say about the answer? Draw out that it would be half as big. What if we multiplied 70 by 16? Draw out that the answer would be twice as big as the answer to 35 × 16. What if we multiplied 70 by 8? Agree that the answer would be the same as to 35 × 16. We get the same answer! So if we halve one number and double the other, this can make the multiplication quicker to work out. Why do you think this works well when multiplying multiples of 5 by even numbers? Draw out that multiples of 5 are easy to double, and even numbers will give a whole answer when halved. Write 14 × 75 on the board. Work with a partner to use our halving and doubling method to find the answer. Which number are you going to halve? Show chn 14 × 75 on a calculator to show that the answer is the same. Write 72 × 25 on the board. 72 is a much bigger number, but our halving and doubling method can still be helpful. If we halve 72 and double 50, we get 36 × 50. But we can halve and double again and get 18 × 100 which is really easy! So if we are multiplying by 25, it can be helpful to double and halve twice. Write 75 × 24 on the board. We can keep halving and doubling until we get to a multiplication we like! 75 × 24 = 150 × 12 =300 × 6 Group of 4-5 children Show chn a rectangle on squared paper measuring 35 across and 16 down. How could we find the area of this rectangle? Fold the rectangle in half horizontally, and cut it into two. Rearrange the two halves of the rectangle to make a 70 by 8 rectangle. What are the measurements of this new rectangle? Has the area changed? No, so 16 × 35 = 8 × 70. Ask chn to work in pairs to make a rectangle measuring 28 by 35, and then to use this to make other rectangles with the same area, recording the measurements of each. Easier: Chn make a 16 by 25 rectangle. Harder: Chn’s rectangles could include those with sides, which are not whole numbers. Chn use halving and doubling to work out the following: 18 × 85, 55 × 24, 75 × 32, 65 × 48, 75 × 48 and 75 × 56. Easier: Chn use halving and doubling to work out 12 × 25, 16 × 25, 18 × 25, 24 × 25, 12 × 35 and 24 × 35. Harder: Chn use halving and doubling to work out 65 × 48, 75 × 48 and 75 × 56. They then discuss whether the strategy of halving and doubling is useful or not, to solve the following: 75 × 44, 75 × 32 and 75 × 42. They discuss and then write what sorts of numbers lend themselves to this strategy. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Squared paper Y6 Maths TS9 – Sum – 5days Repeat with 65 × 24: 65 × 24 = 130 × 12 = 260 × 6 = 520 × 3 We can work 520 × 3 out easily in our heads! Write 4.92 × 3 on the board. What do you think the answer will be approximately? Draw out rounding 4.92 to 5 and then multiplying by 3. Will the true answer be more than 15 or less than 15? Why? We can use the grid method to help us to find the exact answer. Work together to complete the grid. How can we work out 3 lots of 0.9? What are 3 lots of 9? 3 times 0.9 will be one tenth of this. × 4 0.9 0.02 3 12 2.7 0.06 14.76 Ask chn to work in pairs to work out 4.23 × 6. Before you start, what do you think the answer will be approximately? Will the true answer be more or less than this? Afterwards take feedback and ask chn to explain how they worked out each part, particularly 6 lots of 0.2 and 6 lots of 0.03. Six lots of three hundredths gives eighteen hundredths, how do we write this? Group of 4-5 children Write 4.28 × 5 on the flipchart. We could use the grid method to work this out, but can you think of another way? Draw out using the strategy of doubling and halving as in the previous session: 4.28 × 5 is the same as = 2.14 × 10 Now it’s easy! What if it was 4.28 × 25? Talk to your partner about how you might find the answer. Draw out that 4.28 × 25 is the same as 2.14 × 50 which is the same as 1.07 × 100 It looked like a multiplication where you would go and find a calculator but actually it turned out to be one you would work out mentally! If the whole part of the number, and the number of hundredths are divisible by four, meaning they can be halved twice quite easily, then multiplying by 25 is easy. Ask chn also to multiply 8.56, 4.36 and 12.64 by 25 using the same method. Easier: Chn multiply the same numbers by 5, not 25. Chn work in pairs to solve the following: 4.21 × 5, 6.42 × 3, 5.32 × 4, 3.64 × 5, 4.84 × 6, 5.46 × 3, and then at least three of their own similar multiplications. Ask them to round each number to the nearest whole to find an approximate answer. Easier: Chn work in pairs to multiply three-digit numbers with one decimal place by single-digit numbers: 42.1 × 5, 64.2 × 3, 53.2 × 4, 36.4 × 2, 48.4 × 6, 54.6 × 5. Ask them to round each number to the nearest whole to help them to find an approximate answer. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS9 – Sum – 5days Write 28 ÷ 3.5 on the board. Talk to your partner about how we could work this out. Draw out that we could count up in steps of 3.5, or record these on an empty number line to help. Draw a line from 0 to 28 and record steps of 3.5 and conclude that there are eight 3.5s in 28. How many 7s are in 28? How does that compare with how many 3.5s are in 28? Discuss how there are twice as many 3.5s in 28 as 7s as each step is half the size. Write 63 ÷ 4.5 on the board. Ask chn to discuss with their partner how they could find the answer. Take feedback, agree that there are seven 9s in 63, and so there must be 14 4.5s, twice as many as each step is half the size. How many 2.25s do you think might be in 63? Why? Use a calculator to check. Write 22 ÷ 4 on the board. How many 4s are in 18? There are two left over, this is half of a group of 4, so if we want an exact answer, there are 5 and a half groups of 4 in 18. Record 22 ÷ 4 = 5½. How else can we write this? Agree that it can be written as 5.5 Group of 4-5 children When we were multiplying certain numbers together, we found it helpful to halve one and double the other. Does this work with division? Let’s try with 28 ÷ 3.5. We could double 3.5 and halve 14, so we get 14 ÷ 7. Mm, we’d get an answer of two, this is much too small. Why is that? Talk to your partner. Draw out that the steps are bigger, and the number being divided is smaller so this gives a much smaller answer. Has anyone got any other ideas? Try doubling both numbers. This seems to work, why? Discuss that as the steps are twice as big, the number being divided needs to be twice as big as well to give the same answer. Try and see if doubling both numbers works with 63 ÷ 4.5 and 30 ÷ 2.5. How could we check our answers? Encourage chn to use multiplication to check. Easier: Try smaller numbers to begin with e.g. 10 ÷ 2.5 and 7 ÷ 3.5 where chn may more readily see that the answer seems reasonable/unreasonable when doubling both/doubling and halving. Group of 4-5 children Display the following word problems: Mr Baker has 50 buns left. He puts them in packs of 8. How many packs can he fill? Ask chn to work in pairs to solve the following: 45 ÷ 2.5, 24 ÷ 1.5, 33 ÷ 1.5, 40 ÷ 2.5, 35 ÷ 3.5, 49 ÷ 3.5, 27 ÷ 4.5, 81 ÷ 4.5 and 54 ÷ 4.5. Easier: Chn may feel more confident to draw jumps of multiples of 0.5. Harder: Also challenge chn to work out; 45 ÷ 1.25, 40 ÷ 2.25 and 49 ÷ 1.75. Ask chn to work out the following divisions giving their answers as vulgar fractions and also as decimal fraction where the conversion is easy to do: © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS9 – Sum – 5days Draw a number line from 0 to 22. Draw five jumps of 4 to 20. Draw another jump of 4, overshooting 22. If we had another jump of four that would get us to 22, but we only need half of that jump to get us to 20. Imagine if you had 22 donuts to share between four people. How many would they get each? They would give five each, and there are two left over, which could be cut in half, so that they get another half each. If £22 was to be shared between four children, how much would they get each? Discuss how we could halve and halve again to find that each child would get £5.50 each. Write 25 ÷ 3. How many threes are in 25? There is 1 left over, this is a third of a group of 3, so the exact answer if 8 1/3. What if it was 26 divided by 3? Write 27 ÷ 4. How many 4s in 27? How much left over? What fraction of four is this? How can we write the answer? Draw out that the exact answer can be written as 6¾, or 6.75. Repeat with 50 ÷ 6 and agree the answer as 8 and 2/6. We could also write this as 8 and a third or 8 point three recurring. Mrs Holes is organising a barbeque. She needs to buy 50 buns. They come in packs of 8. How many packs does she need to buy? Mrs Merttens has eight children. She gives them £50 to share between them. How much will they get each? A length of 50cm ribbon is cut into eight equal strips. How long is each strip? 50 sandwiches are shared equally between eight hungry children. How many can they have each? Ask chn to read each word problem and discuss the calculation needed. Agree that every problem requires the calculations 50 ÷ 8, but discuss how the answer to each is needed in a slightly different way, rounded up, rounded down, as a fraction, as a decimal. Harder: Ask chn to come up with other number stories which need the answers in different forms. 33 ÷ 4, 21 ÷ 5, 29 ÷ 5, 28 ÷ 6, 28 ÷ 3, 38 ÷ 3, 45 ÷ 10, 53 ÷ 10, 47 ÷ 7, and 58 ÷ 8. They then choose two numbers between 50 and 100 to divide by 4, 5 and 8. Easier: Chn choose four numbers between 20 and 30 to divide, by 3, 4 and 5. Harder: Encourage chn to express the fractions in their simplest form, e.g. 28 ÷ 6 = 4 2/3. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS9 – Sum – 5days