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Year 5 Term 2 Unit 9. Day 1. L.O.1 To be able to add and subtract any pair of two-digit numbers. 30+40 Write the answer in your books. 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

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slide2
L.O.1

To be able to add and subtract any pair of two-digit numbers

slide3
30+40

Write the answer in your books.

slide4
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

slide5
Try these using the same method where possible:

80 – 50

70 + 40

34 + 54

75 – 40

46 + 52

58 – 25

80+ 40

slide7
L.O.2

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

slide8
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.

slide9
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?
slide10
Our sum is:

93 – 69 = ( 93 – 70 ) + 1

= 23 + 1

= 24

This can be shown on a number line.

+1 -70

23 24 93

slide11
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

slide12
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

slide13
Try this:

286 – 97 = (286 – 100) + 3

= 186 + 3

= 189

We need a volunteer to draw the number line!

slide14
Try this:

5250 – 1998 = (5250 – 2000) + 2

= 3250 + 2

= 3252

We need a volunteer to draw the number line

slide15
Try this

458 + 199 = (458 + 200) – 1

= 658 – 1

= 657

We need a volunteer to draw the number line

slide16
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

slide17
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?

slide18
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

slide20
L.O.1

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

slide21
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

slide22
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

slide23
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?

slide24
Q. Did you see the similarities?

Q. What strategies did you use?

slide25
L.O.2

To be able to add several numbers.

slide26
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?

slide27
To find the total we can;

1. look for numbers that sum 100

60 + 40

2. start with the largest number first

90 + 60 +

slide28
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?

slide29
Look at this calculation:

63 + 15 + 35

Q. What strategies do you use?

slide30
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

slide31
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.

slide33
Q. How many pairs of numbers sum to 10?

1 + 2 + 3 + 4 + 5 + 5+ 6 + 7 + 8 + 9

= 5 X 10

slide34
Look at this calculation:

4 + 4 + 3 + 5

Q. What multiplication is this equivalent to?

slide35
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?

slide37
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

slide38
Let’s look at this one

48 + 49 + 50 + 51 + 52

Q. What strategies could we use to find the sum?

slide39
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

slide40
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

slide41
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

slide43
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.
slide45
L.O.1

To be able to add near doubles including decimals.

slide46
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.

slide47
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

slide49
Now work out these calculations

17 + 16 and 1.7 + 1.6

Q. How did you work them out?

slide50
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?

slide51
The answer is simple.

If 16 +17 = 33

then 1.6 + 1.7 = 3.3

We have divided 33 by 10

OR

moved the decimal point one place to the left.

slide52
In your books work out the following using the same method

12 + 13 1.2 + 1.3

25 + 24 2.5 +2.4

44 + 43 4.4 + 4.3

TiP : do the whole numbers first

slide53
The answers are:

25 2.5

49 4.9

87 8.7

slide54
L.O.2

To be able to add several numbers using a variety of strategies for mental addition.

To solve mathematical problems or puzzles, recognise and explain patterns and relationships.

slide62
Q What do you think would happen if we subtract 7 from each number?

Would it still be a magic square?

slide80
Q Will every diagonal of 4 total 46?

On your on sheet highlight 4 diagonals and test.

slide82
L.O.2

To be able to add several numbers using a variety of strategies for mental addition.

To solve mathematical problems or puzzles, recognise and explain patterns and relationships.