Year 6 Teaching Sequence 3 - Written methods for multiplication and division (five days) Prerequisites: Use the grid method to multiply two-digit numbers by two-digit numbers and three-digit numbers by single-digit numbers (see Year 5 Summer teaching sequence 4) Use chunking on the ENL to divide three-digit numbers by single-digit numbers, including those leaving a remainder (see Year 5 Summer teaching sequence 4) Revise all multiplication and division facts for the 2 to 10 times tables (see oral and mental starter banks 2 and 3) Approximate first when multiplying and dividing (see oral and mental starter bank 3) Overview of progression: Children revise multiplying two-digit numbers by two-digit numbers and three-digit numbers by single-digit numbers, and dividing three-digit numbers by single-digit numbers, approximating first. They move on to multiply four-digit numbers by single-digit numbers and extend dividing three-digit numbers by single-digit numbers to include those with larger answers than in Year 5. Given word problems, they decide whether to round answers up or down after division. Children use the relationship between multiplication and division to find missing numbers. Note that in Hamilton sequences the ENL is used to record the steps in chunking in Years 4 and 5. This is the first time that the vertical layout has been introduced. Children are given the choice of which to use throughout Year 6. Note that the most efficient chunking when recording using the vertical layout looks very similar to traditional long division on paper, but the process is easier to understand. Watch out for children who learn to use the grid method by just multiplying all the parts together but who don't understand why, particularly when multiplying two-digit numbers together. Encourage them to see what is worked out on © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS3 – Aut – 5days each row, so in 45 × 23 for example, the first row is 45 × 20, worked out in two stages, and the second row is 45 × 3, again worked out in two stages, and the two rows are added together. Watch out for children who repeatedly draw jumps of 10 lots of the divisor when chunking, rather than biggest multiple of ten that they can, e.g. they draw six lots of jumps of 30, rather than one big jump of 180 when dividing 188 by 3. This will become very inefficient when the calculations need 7, 8 or 9 such jumps. Encourage them to write a list of multiples of ten of the divisor (e.g. 30, 60, 90, 120, 150, 180…). © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS3 – Aut – 5days Objectives: Multiply pairs of multiples of 10, e.g. 30 x 40, or of 10 and 100, e.g. 600 x 40 Approximate first before calculating Revise using the grid method to multiply three-digit numbers by single-digit numbers and to multiply two-digit numbers by two-digit numbers Use the grid method to multiply four-digit numbers by single-digit numbers Revise using chunking on the ENL to divide three-digit numbers by single-digit numbers, including those leaving a remainder Decide whether to round up or down after division Whole class Group activities Paired/indiv practice Resources Write 7 x 426 on the board and ask chn to discuss in pairs an estimate for the answer. Take feedback, drawing out different strategies. If we round 426 to 400 and find seven lots of 400, this would give an estimate of 2800. Will the true answer be more or less than this? If we round up, 500 multiplied by 7 is 3500, and the true answer will be about a quarter of the way towards this number. Sketch an ENL to show 2800 and 3500. So perhaps the true answer might be closer to 3000 than 2800. Ask chn to use the grid method to find the answer, and then compare it with their estimates. × 400 20 6 Group of 4-5 children Prepare a flipchart with workings out for grid multiplications 6 x 683, 723 × 8 and 37 × 23, using Post-its™ to cover the numbers being multiplied together, e.g. □ □ □ × Ask chn to work in pairs to discuss estimates. They record their estimates and then use the grid method to find the true answers (see resources). Easier: Slightly easier activity sheet (digits 6, 7, 8 and 9 used less frequently as these are likely to be times tables chn are not so secure with). Harder: Chn choose five and make an estimate for each. Challenge them to complete them accurately in five minutes. Then challenge them to come up with a two-digit by two-digit multiplication with an answer as close to 3500 as they can, neither number can be a multiple of ten. Activity sheets (see resources) 7 2800 140 42 2982 Explain that with multiplication, our estimates are not as accurate when estimating the □ 3600 480 18 4098 Ask chn to discuss in pairs what numbers might be hidden. Could the left-hand single-digit numbers be 5? Why not? Look at the 18. What other numbers can’t it be? What numbers could it be? Agree 2, 9, 3 and 6. Do any of these fit with the products, 3600 and 480? What numbers have a product of 36 and 48? Repeat for 723 × 8 and 37 × 23. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS3 – Aut – 5days answers to subtractions and addition. This is because the effect of multiplication is to magnify the effects of rounding. Repeat with 738 × 6. 700 multiplied by 6 is 4200, 800 × 6 is 4800; the true answer is likely to be about a third of the way between the two, so about 4400. Use the grid method to find out. Repeat with 24 x 67. Take feedback. 20 times 70 is 1400. The answer is likely to be more than this. 25 multiplied by 70 might give a closer estimate. What are seven 25s? And seventy 25s? Will the true answer be more or les than this? So the true answer will be a bit less than 1750, but more than 1400. Repeat with 52 × 48. 50 multiplied by 50 is 2500, will the true answer be more or less than this? It’s not so difficult to say this time! (You could explain that when we rounded 52 down to 50, we subtracted two lots of 48, and then when we rounded 48 up to 50 we added two lots of 50, so the true answer will be a little more than 2500, but 2500 is probably a close enough estimate!) Ask chn to use the grid method to find out. Write 29 x 51 on the board. Discuss an estimate with your partner. Take feedback. Discuss how you could use the grid method to find the answer, or you could find 30 lots of 51, and then subtract one lot of 51 to find the answer, recording a few jottings along the way. Easier: Don’t cover the second number in the multiplication, i.e. those on the right of the grid, i.e. 6, 8 and 23. Remind them that the first top numbers is a multiple of 100, a multiple of 10 and the last one a single-digit number in the first multiplication. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS3 – Aut – 5days Write 3 x 4235 on the board and ask chn to discuss in pairs how they might find the answer. Take feedback and discuss how the grid method could be used, this time with an extra column. Ask chn to work in pairs to use the grid method to find the answer. Write 2137 × 6 on the board. Discuss with your partner what might be a good estimate for this product. Take feedback. 2000 multiplied by 6 is 12,000, and if we multiply the rest of the number by 6, we’re probably going to get near another 1000, so 13,000 would be a good estimate. Ask chn to use the grid method to find the true answer. Repeat with 7 x 6423. Group of 4-5 children Write 3 x £4.72 on the flipchart. How could we use the grid method to find the answer? What would be a rough estimate? Together work through using the grid methods to find the answer: × £4 70p 2p 3 £12 £2.10 6p £14.16 Ask chn to use the grid method to find 6 x £5.45. How could we use the grid method to find 3 x £24.72? Talk to your partner and sketch the grid on your whiteboard. Take feedback. Then demonstrate × £20 £4 70p 2p 3 £60 £12 £2.10 6p £74.16 Ask pairs to make up three of their own four-digit prices and multiply them by single-digit numbers. Which was the easiest? Why? And the most difficult? Why? Easier: Keep to three-digit prices and avoid digits such as 7 and 8 if chn are unsure of these times tables. Harder: When thinking of their own multiplications, say that the answers must be over £100. Ask chn to work in pairs to discuss estimates. They record their estimates and then use the grid method to find the true answers (see resources). Easier: Slightly easier activity sheet (digits 6, 7, 8 and 9 used less frequently as these are likely to be times tables chn are not so secure with). Harder: Chn choose five and make an estimate for each. Challenge them to complete them accurately in five minutes. Then challenge them to come up with a four-digit by single-digit multiplication with an answer as close to 20,000 as they can, the four-digit number cannot be a multiple of 10, 100 or 1000. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Activity sheets (see resources) Y6 Maths TS3 – Aut – 5days Write 327 ÷ 5 on the board. How many 5s do you think might be in 327? More than ten? More than twenty? Record the multiples of 50, 100, 150… 350. So they are more than sixty lots of five, but fewer than seventy. So our first chunk can be 300. Ask chn to draw with ENL jotting to work out the division. Take feedback, revising any steps they have forgotten. Now write the following jottings on the board: 5 lots of 7 60 lots of 7 0 420 r1 455 456 456 ÷ 7 = 65 r 1 - 456 420 - 36 35 (60x7) Group of 4-5 children Work in pairs to write a three-digit by single-digit division with an answer between 30 and 40. Be prepared to tell the group how you came up with your division. Take feedback. Draw out finding 30 lots and 40 lots of 6 for example, and then choosing a number between these two products to divide by 6. Find another division with a different divisor with an answer between 30 and 40. Take feedback Now think of two divisions with an answer between 40 and 50. Easier: Think of a three-digit by singledigit division with an answer of between 10 and 20, then 20 and 30. Harder: Think of a three-digit by single-digit division with an answer of between 70 and 80, then 80 and 90. Chn practise using both layouts for chunking for four calculations and then choose their favourite to use for others (see resources). Easier: Slightly easier activity sheet (digits 6, 7, 8 and 9 used less frequently as these are likely to be times tables chn are not so secure with). Ensure that chn list multiples of ten of the divisor to help them with the estimate and the first chunk. Activity sheets (see resources) (5x7) 1 65 456 ÷7 = 65 r 1 Two chn have worked out 456 divided by 7. These are their jottings. Look at each and discuss with your partner what you think they have done. Draw out that the first layout looks © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS3 – Aut – 5days familiar, and that the second is not. Why has the second child written 420? And then 60x7 in brackets? What have they done then? How does this relate to the number line jotting? Draw out that the child has subtracted 420 from 456 to find how much is left on the number line. Ask chn to work in pairs to use both layouts to work out 327 ÷ 6, and then 445 ÷ 8. These are two layouts of just different ways of recording the steps in chunking, which did you prefer? Display the following problem: An apple picker has picked 153 apples. They are to be packed into trays of four apples. How many full trays can be packed? Ask chn to discuss it in pairs. What calculation needs to be worked out? 153 ÷ 4 Work it out on your whiteboards. 153 - 120 (30 x 4) 33 – 32 (8 x 4) 1 So what’s the answer to the problem? 38 r 1 Discuss how only 38 trays will be filled, and so for this word problem we round the answer down. Display the following problem: A primary school needs 145 apples for their healthy snack times this week. How many Group of 4-5 children We divided 153 by 4 and got an answer of 38 r 1. How could we check that this is correct? Draw out using multiplication. What multiplication would we need to do? Together work out 4 x 38: = (4 x 30) + (4 x 8) = 120 + 32 = 152 But this is 152 not 153? Discuss how we need to add the remainder of 1 on, and so would get 153. Ask chn to work in pairs to do and then check the following: 260 ÷ 6 = 43 r 2 382 ÷ 7 = 56 r 2 345 ÷ 9 = 37 r 3 389 ÷ 8 = 48 r 5 Chn work through problems, finding solutions and deciding whether answers to the required calculations need rounding up or down (see resources). Easier: Slightly easier activity sheet (with easier calculations). Harder: Ask chn to write ‘up’ or ‘down’ by the side of each problem, and choose four to work out, plus the last one. Then set them the following challenge: A long distance walker is attempting to walk round the coast of Britain, a total of 9471 miles. He will walk for eight hours per day. He walks at three miles per hour. How many hours would it take? How many days? Weeks? Months? © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Activity sheets of word problems (see resources) Y6 Maths TS3 – Aut – 5days packs need to be ordered? Ask chn to discuss it in pairs, work out the necessary calculation (145 ÷ 4), then to answer the problem. Take feedback. Did you need to round up or down this time? (Up) Write □ ÷ 6 = 87 on the board. Discuss with your partner how we could find the missing number. Take feedback; draw out multiplying 87 by 6 to find the number that was initially divided. Ask chn to find this product and then use chunking to check that the division does indeed work. 522 ÷ 6 522 – 480 (80 x 6) 42 – 42 (7 x 6) So the answer is indeed 87. Repeat with □ × 7 = 48. Write □ × 8 = 416 on the board. Discuss with your partner how we could find the missing number. Take feedback; draw out dividing 416 by 8 to find what number was multiplied by 8. Ask chn to work out the division and then to multiply to check that this does work. Repeat with □ × 7 = 392. Easier: Check: 137 ÷ 6 = 23 r 5 96 ÷ 7 = 23 r 5 113 ÷ 4 = 28 r 3 172 ÷ 8 = 22 r 4 Group of 4-5 children Show chn 25 × 25 using the ITP Multi Grid: If I increase the first 25 by one, and decrease the second 25 by one, to make the multiplication 26 multiplied by 24, do you think I will get the same answer? Discuss this with your partner. Write down the product 625 to keep a record of it. Increase the first 25 to 26 by using the toggle. How much has been added? Now decrease the second 25 by one. And how much has been subtracted? What's the new product? Repeat with 50 × 50 and another pair of numbers of the chn’s choice. Ask chn to use the digits 5, 6, 7, 8 and 9 to make four-digit by single-digit multiplications and divisions, and two-digit by twodigit and four-digit multiplications, at least two of each type of calculation. Easier: Use digits 4, 5, 6 and 7 to make three-digit by single-digit multiplications and divisions, and two-digit by two-digit multiplications. Harder: Challenge chn to find the greatest and least answer for each type of calculation. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. ITP Multi Grid Y6 Maths TS3 – Aut – 5days Easier: Use the ITP to show 325 × 5. If I increase the 5 to 6, how will the product change? How much will be added? What if I increase it to 7? How do you know? What if I change it from 5 to 4? Repeat with similar multiplications. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y6 Maths TS3 – Aut – 5days