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# Year 5 Term 2 Unit 9

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1. Year 5 Term 2 Unit 9 Day 1

2. L.O.1 To be able to add and subtract any pair of two-digit numbers

4. Q. How did you work that out? We can get the answer using: the number fact 3 + 4 and then applying place value x 10 We can use a similar method for subtraction LOOK…. 50 – 20 The number fact is 5 – 2 And the place value is x 10

5. Try these using the same method where possible: 80 – 50 70 + 40 34 + 54 75 – 40 46 + 52 58 – 25 80+ 40

6. L.O.2 To be able to add or subtract the nearest multiple of 10 ,100 or 1000 then adjust.

7. Round these numbers: 1. To the nearest 10 34277866 55 2. To the nearest 100 16776135485521 3. To the nearest 1000 243573284982 6525 7721 Write in your books how much we had to adjust each number by.

8. We can use rounding as a strategy for addition and subtraction. 93 – 69 Thus: • What multiple of 10 is nearest to 69? • What is 93 – 70? • Have we subtracted more or less than 69? • How should we adjust the answer to make it correct?

9. Our sum is: 93 – 69 = ( 93 – 70 ) + 1 = 23 + 1 = 24 This can be shown on a number line. +1 -70 23 24 93

10. Our sum is now: 93 – 69 = ( 93 – 70 ) + 1 = 23 + 1 = 24 This can be shown on a number line. -70 + 1 23 24 93

11. We are going to try this: 368 + 51. 368 + 51 = (368 + 50) + 1 = 418 + 1 = 419 Draw the number line in your books. +50 +1 368 418 419

12. Try this: 286 – 97 = (286 – 100) + 3 = 186 + 3 = 189 We need a volunteer to draw the number line!

13. Try this: 5250 – 1998 = (5250 – 2000) + 2 = 3250 + 2 = 3252 We need a volunteer to draw the number line

14. Try this 458 + 199 = (458 + 200) – 1 = 658 – 1 = 657 We need a volunteer to draw the number line

15. Do these : include the written sum and the number line. All groups: + Spheres + Prisms 289 – 98756 – 1972348 – 1996 645 + 69 572 + 1965932 + 2995 584 – 97 615 - 498 3688 - 1994 1267 + 88 1546 + 9975482 + 1988

16. Look at these: 73 + 26182 – 95 6003 – 599456 – 29 73 + 200 583 – 71 • For which of these would you use the rounding and adjusting strategy? Q . How would you tackle the other questions?

17. By the end of the lesson the children should be able to: For example, work out mentally that: 274 + 96 = 370 as 274 + 100 – 4 = 374 – 4 = 370 and 4005 – 1997 = 2008 as 4005 – 2000 + 3

18. Year 5 Term 2 Unit 9 Day 2

19. L.O.1 To be able to recall addition and subtraction facts for each number to 20 and extending to multiples of 10.

20. Write the answer in your books to the following: 15 – 712 + 89 + 8 3 + 4 7 + 611 + 1114 – 5 12 – 46 + 138 – 517 + 6 19 – 10

21. Q. What strategies can we use for quick recall? We can : 1. double and subtract or add e.g. 6 + 7 = 6 + 6 +1 2. round up or down and subtract or add the difference e.g. 8 + 12 = 8 + 10 + 2 • Subtract even numbers by halving it and subtracting it twice e.g. 16 – 4 = 16 – 2 - 2

22. We can use the same strategies with multiples of 10. Do these in your book: 70 + 6010 +20140 – 50190 – 100 Can you see the similarities?

23. Q. Did you see the similarities? Q. What strategies did you use?

24. L.O.2 To be able to add several numbers.

25. 40 + 90 + 60 + 50 Copy these numbers into your book as they are here and calculate the total. Q. How did you find the total?

26. To find the total we can; 1. look for numbers that sum 100 60 + 40 2. start with the largest number first 90 + 60 +

27. Now try these: 60 + 70 + 20 + 80 + 20 + 30 + 80 + 70 50 + 60 + 30 + 80 + 40 + 90 + 40 + 50 Q. What strategies did you use?

28. Look at this calculation: 63 + 15 + 35 Q. What strategies do you use?

29. To find the total we can; 1. look for unit pairs that make 10 35 + 15 2. start with the largest number first 63 + 35

30. 1 + 2 + 3 + 4 + 5 + 5+ 6 + 7 + 8 + 9 Copy these numbers into your book and add them up. Remember to use pairing strategy.

32. Q. How many pairs of numbers sum to 10? 1 + 2 + 3 + 4 + 5 + 5+ 6 + 7 + 8 + 9 = 5 X 10

33. Look at this calculation: 4 + 4 + 3 + 5 Q. What multiplication is this equivalent to?

34. To find the answer we must first do the calculation using our addition strategies. 4 + 4 + 3 + 5 = 16 16 is the equivalent to 4 X 4 Q Who got this right?

35. To find the answer we must first do the calculation using our addition strategies. 18 + 20 + 22 When we look at the numbers we can see that 18 and 22 make 40 ; a multiple of 20 20 is also a multiple of 20 That means that there are 3 multiples of 20 so 60 is the equivalent to 20 X 3

36. Let’s look at this one 48 + 49 + 50 + 51 + 52 Q. What strategies could we use to find the sum?

37. To find the total we can; 1. look for numbers that sum 100 48 +52 2. start with the largest number first 52 + 51 + 3. look for multiples 50 4. look for unit pairs of 10 51 + 49

38. Showing your method, do the following in your books: 18 + 19 + 20 + 21 + 22 26 + 28 + 30 + 32 + 34 64 + 66 + 70 + 74 + 76 83 + 85 + 90 + 97 + 95

39. Q. What strategies did you use to find the answers? Q. Which strategy do you think is best for this calculation? 18 + 19 + 20 + 21 + 22

40. Copy this into your books

41. In your books write down sets of numbers from the table that you can total using all the addition strategies we have looked at today.

42. Year 5 Term 2 Unit 9 Day 3

43. L.O.1 To be able to add near doubles including decimals.

44. Look at this calculation 35 + 36 Q What strategy could you use to find the sum? Look at the numbers, they are near doubles of each other.

45. To calculate the sum we simply have to double one of the numbers and adjust the answer. E.g. 35 + 36 = (35 x 2) +1 70 + 1 = 71 OR 35 + 36 = (36 x 2) -1 72 – 1 = 71

46. Try these using one or all of the near doubling strategies: 41 + 42 = 85 + 82 = 53 + 50 = 11 + 15 =

47. Now work out these calculations 17 + 16 and 1.7 + 1.6 Q. How did you work them out?

48. To find the sum of 16 + 17 we double and adjust the numbers. 16 x 2 = 32 32 + 1 = 33 If 16 is the same as 1.6 x 10 and 17 is the same as 1.7 Q. How can this help us work out 1.6 + 1.7?