Multiplication and Division Double and halve 2- and 3-digit numbers

1. Multiplication and Division Double and halve 2- and 3-digit numbers Objectives Day 1 Double and halve 2-digit numbers, including odd numbers. Day 2 Double and halve 3-digit numbers. Year 4

2. Multiplication and Division Double and halve 2- and 3-digit numbers Starters Day 1Double the numbers 1 to 20 and find the corresponding halves (pre-requisite skills) Day 2Double and halve multiples of 100 (pre-requisite skills) Year 4

3. Multiplication and Division Double and halve 2- and 3-digit numbers StarterDouble the numbers 1 to 20 and find the corresponding halves Top Marks doubles and halves Year 4

4. Multiplication and Division Double and halve 2- and 3-digit numbers StarterDouble and halve multiples of 100 Year 4

5. Multiplication and Division Double and halve 2- and 3-digit numbers Objectives Day 1 Double and halve 2-digit numbers, including odd numbers. Year 4

6. Day 1:Double and halve 2-digit numbers, including odd numbers. Let’s double 26. We can partition 26 into 10s and 1s. and double each part. Double 20 is ? 12 40 40 + 12 = 52 Double 6 is ? 40 + 12 = ? Double 26 Now choose three more 2-digt numbers and double them. • Can you find one that totals more than 100? Year 4

7. Day 1:Double and halve 2-digit numbers, including odd numbers. Let’s try 75. Double 70 is ? Double 5 is ? 10 140 140 + 10 = 150 Double 75 is ? Now 84. Double 75 Double 84 Double 80 is ? 160 8 Double 4 is ? 160 + 8 = 168 Double 84 is ? Year 4

8. Day 1:Double and halve 2-digit numbers, including odd numbers. Now let’s find half of 26. Half of 20 is ? 10 3 10 + 3 = 13 Half of 6 is ? Half of 26 is ? Half of 26 Now on your whiteboards find half of 34 and half of 96. • What makes those a bit trickier? Year 4

9. Day 1:Double and halve 2-digit numbers, including odd numbers. Let’s check those. 15 2 45 3 15 + 2 = 17 45 + 3 = 48 Half of 34 Half of 96 What do you notice about the 10s in those two questions? Year 4

10. Day 1:Double and halve 2-digit numbers, including odd numbers. Now let’s see what happens when the 1s digit is odd. 10 11/2 10 + 11/2 = 111/2 Half of 23 Now on your whiteboards find half of 47 and half of 59. • How can you halve the odd 1s digit? Year 4

11. Day 1:Double and halve 2-digit numbers, including odd numbers. Let’s check those. 20 31/2 25 41/2 Half of 47 Half of 59 20 + 31/2 = 231/2 25 + 41/2 = 291/2 Who can talk us through this one? And this one? Year 4

12. Challenge Year 4

13. Multiplication and Division Double and halve 2- and 3-digit numbers Objectives Day 2 Double and halve 3-digit numbers. Year 4

14. Day 2:Double and halve 3-digit numbers. 100 200 400 1400 800 1600 1000 1800 1200 600 2000 Let’s check through the doubles of 100s numbers. 200 300 400 500 We can use these to help us double 3-digit numbers! 600 700 800 900 1000 Year 4

15. Day 2:Double and halve 3-digit numbers. Let’s try double 226. Partition into 100s, 10s and 1s. 400 40 12 400 + 40 + 12 = 452 Double 200 is ? Double 20 is ? Double 226 Now on your whiteboards find double 471 and double 638. Double 6 is ? Three numbers to add this time! Year 4

16. Day 2:Double and halve 3-digit numbers. Who can talk us through this one? 800 140 2 800 + 140 + 2 = 942 And this one? Double 471 Double 638 Careful with the addition! 1200 60 16 1200 + 60 + 16 = 1276 Year 4

17. Day 2:Double and halve 3-digit numbers. We can find HALF of 3-digit numbers in the same way. 100 10 3 Half of 200 is ? 100 + 10 + 3 = 113 Half of 20 is ? Half of 6 is ? Half 226 Now on your whiteboards find half of 326, 452 and 643. Half of 226 is ? Be careful with any odd digits! Year 4

18. Day 2:Double and halve 3-digit numbers. Let’s check. Who can talk these through? 150 10 200 25 300 20 3 1 11/2 150 + 10 + 3 = 163 200 + 25 + 1 = 226 300 + 20 + 11/2 = 3211/2 Half 643 Half 326 Half 452 The 100s digit in 362 is odd. The 10s digit in 452 is odd. The 1s digit in 643 is odd. Year 4

19. Day 2:Double and halve 3-digit numbers. Let’s work together to find half of 531. 250 15 1/2 What do you notice about the digits in 531? 250 + 15 + 1/2 = 2651/2 Half of 500 is ? Half 531 Half of 30 is ? Half of 1 is ? Half of 531 is ? Year 4

20. Challenge Year 4

21. Multiplication and Division Double and halve 2- and 3-digit numbers Well Done! You’ve completed this unit. Objectives Day 1 Double and halve 2-digit numbers, including odd numbers. Day 2 Double and halve 3-digit numbers. Year 4

22. Multiplication and Division Unit 1 Problem solving and reasoning questions Write two sentences to relate these three numbers: 37, 74 and 148. Use a jotting to double these numbers: (a) 216 (b) 327 (c) 438 Can you describe a pattern in the answers? We know double 30 is 60 and double 8 is 16. So what is half of 76? Explain in a sentence why a jotting is helpful when we find half of 318. Year 4

23. Problem solving and reasoning answers Write two sentences to relate these three numbers: 37, 74 and 148. e.g. 2 x 37 = 74, 2 x 74 = 148, 74 ÷ 37 = 2 etc. Use a jotting to double these numbers: (a) 216 432 (b) 327 654 (c) 438 876 Can you describe a pattern in the answers? The differences between the initial numbers is 111, the answers have a difference of 222. Where children have made errors with doubling 3-digit number, it is often the result of treating digits of the number as a single digit, ignoring place value. This would produce an answer of 18 or 34 for (a). It is useful to get children to estimate first We know double 30 is 60 and double 8 is 16. So what is half of 76? 38 Explain in a sentence why a jotting is helpful when we find half of 318. A jotting helps keep track of each part of the partitioned number. So, half of 300 is 150, half of 10 is 5 and half of 8 is 4. It also reminds us to recombine these to find the answer: 159. Year 4