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Year 5 Term 2 Unit 9 Day 1

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

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30+40 Write the answer in your books.

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**Q. How did you work that out?**

We can get the answer using: the number fact 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

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**Try these using the same method where possible:**

80 – 50 75 – 40 58 – 25 80+ 40

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**In your book write synonyms for:**

+ -

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

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**Round these numbers: 1. To the nearest 10 34 27 78 66 55**

2. To the nearest 100 3. To the nearest 1000 Write in your books how much we had to adjust each number by.

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**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?

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**This can be shown on a number line.**

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

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**This can be shown on a number line.**

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

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**We are going to try this: 368 + 51. 368 + 51 = (368 + 50) + 1 **

= ( ) + 1 = = 419 Draw the number line in your books.

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

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

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Try this = ( ) – 1 = 658 – 1 = 657 We need a volunteer to draw the number line

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**include the written sum and the number line.**

Do these : include the written sum and the number line. All groups: Spheres Prisms 289 – – – 1996 584 –

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Look at these: – 95 6003 – – 29 – 71 For which of these would you use the rounding and adjusting strategy? Q . How would you tackle the other questions?

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**By the end of the lesson the children should be able to:**

For example, work out mentally that: = 370 as – 4 = 374 – 4 = 370 and 4005 – 1997 = 2008 as 4005 –

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Year 5 Term 2 Unit 9 Day 2

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

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**Write the answer in your books to the following:**

15 – – 5 12 – – 19 – 10

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**Q. What strategies can we use for quick recall?**

We can : 1. double and subtract or add e.g = 2. round up or down and subtract or add the difference e.g = Subtract even numbers by halving it and subtracting it twice e.g. 16 – 4 = 16 – 2 - 2

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**We can use the same strategies with multiples of 10.**

Do these in your book: – – 100 Can you see the similarities?

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**Q. Did you see the similarities?**

Q. What strategies did you use?

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

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Copy these numbers into your book as they are here and calculate the total. Q. How did you find the total?

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**To find the total we can;**

1. look for numbers that sum 100 2. start with the largest number first

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**Q. What strategies did you use?**

Now try these: Q. What strategies did you use?

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**Look at this calculation: 63 + 15 + 35**

Q. What strategies do you use?

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**To find the total we can;**

1. look for unit pairs that make 10 2. start with the largest number first

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**Copy these numbers into your book and add them up.**

Copy these numbers into your book and add them up. Remember to use pairing strategy.

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The answer is 50.

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

= 5 X 10

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**Look at this calculation: 4 + 4 + 3 + 5**

Q. What multiplication is this equivalent to?

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**To find the answer we must first do the calculation using our addition strategies.**

= 16 16 is the equivalent to 4 X 4 Q Who got this right?

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**Q. How can we represent the following as a multiplication?**

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**To find the answer we must first do the calculation using our addition strategies.**

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

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**Let’s look at this one 48 + 49 + 50 + 51 + 52**

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

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**To find the total we can;**

1. look for numbers that sum 100 48 +52 2. start with the largest number first 3. look for multiples 50 4. look for unit pairs of 10

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**Showing your method, do the following in your books:**

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**Q. What strategies did you use to find the answers?**

Q. Which strategy do you think is best for this calculation?

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**Copy this into your books**

20 2 49 23 86 17 64 50 60 38 21 7 40 16 62 42

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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.

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Year 5 Term 2 Unit 9 Day 3

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

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**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.

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**To calculate the sum we simply have to double one of the numbers and adjust the answer.**

E.g = (35 x 2) +1 = 71 OR = (36 x 2) -1 72 – 1 = 71

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**Try these using one or all of the near doubling strategies:**

= = = =

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**17 + 16 and 1.7 + 1.6 Now work out these calculations**

Q. How did you work them out?

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**To find the sum of 16 + 17 we double and adjust the numbers.**

16 x 2 = 32 = 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 ?

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The answer is simple. If = 33 then = 3.3 We have divided 33 by 10 OR moved the decimal point one place to the left.

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

TiP : do the whole numbers first

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The answers are:

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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.

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Look at this table 13 18 11 12 14 16 17 10 15

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**What is the total for this column and this row?**

13 18 11 12 14 16 17 10 15

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**What do you notice about the totals?**

13 18 11 12 14 16 17 10 15

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Yes. They all add up to 42!! 13 18 11 12 14 16 17 10 15

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**Are there any other patterns?**

13 18 11 12 14 16 17 10 15

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Look at these numbers 13 18 11 12 14 16 17 10 15

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**This known as a 3 x 3 magic square.**

13 18 11 12 14 16 17 10 15

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

Would it still be a magic square?

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**Let’s check. What is the ‘magic’ total for the square now?**

6 11 4 5 7 9 10 3 8

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**Yes. It is 21.How could we have predicted this happening?**

6 11 4 5 7 9 10 3 8

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**Would the square still be magic if we aded or subtracted ANY number from each square?**

13 18 11 12 14 16 17 10 15

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**It would have to be the same number from each square.**

13 18 11 12 14 16 17 10 15

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**Let’s look at the number patterns with some different numbers.**

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**Q What do you notice about the answers we have found each square that we have tried?**

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**Each answer we have had has been a multiple of 3!**

13 18 11 12 14 16 17 10 15

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**The total we found (42) is 14 X 3.**

13 18 11 12 14 16 17 10 15

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**Remember when we subtracted 7 from each number**

Remember when we subtracted 7 from each number? The total (21) is 3 x 7…MAGIC 6 11 4 5 7 9 10 3 8

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**What is the sum of the first row and column?**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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**It is 46. Is this a multiple of 4?**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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No. It isn’t. 17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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**Do all the rows and columns total 46?**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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**Yes they do. Can you find any sets of 4 numbers that total 46?**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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**Let’s have a look at some.**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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**This is made up of 4 magic squares put together.**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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**Do these numbers add up to 46?**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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**Q Will every diagonal of 4 total 46?**

On your on sheet highlight 4 diagonals and test.

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**Let’s look at some of your answers.**

17 10 15 4 14 5 16 11 8 19 6 13 7 12 9 18

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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.

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