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Watch: Number bonds to 10

Can you remember what number bonds are? Watch this video to remind yourself.

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How can we show the number bonds to 10?

There are different ways to show bonds to 10, for example we can use a bonds to ten rainbow, like this.

Ten rainbow

We can use 10 frames, like this.

a number frame showing 2 + 8 = 10

Or we can draw on 鈥榢nown number facts鈥. That means that you鈥檝e done so much work on your number bonds to 10 that you just know them.

1 + 9 = 10

2 + 8 = 10

3 + 7 = 10

4 + 6 = 10

5 + 5 = 10

You can use these number facts to work out new ones.

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Example 1

Here is the number 2.

2 counters

Here is 2 made 10 times bigger. How many can you see now?

20 counters

2 multiplied by 10 equals 20.

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Example 2

Here is the number 8.

8 counters

Here is 8 made 10 times bigger. How many can you see?

80 counters

8 multiplied by 10 makes 80.

If I know that 2 + 8 = 10, then I also know that 20 + 80 = 100.

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Example 3

Let's see if this works for other numbers.

We know that 6 + 4 = 10, does that mean 60 + 40 = 100?

Let's look at the 100 square to check.

40 plus 60 on a 100 square

Can you see how the total is 100? 40 blocks are white and 60 blocks are yellow.

There are 100 blocks altogether.

40 + 60 = 100

Have a look at the number line below to see the same sum.

a number line to 100 showing 40 + 60 = 100
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Example 4

What two digit number goes with 55 to make 100?

Let鈥檚 go back to the number line to see how we can solve this.

Here is the number 55 marked on a number line.

55 on a  number line to 100

If you add 5 to 55, it makes 60.

55 plus 5 equals 60 on a numberline

If you add another 40 to 60, you will reach 100.

55 plus 5 plus 40 equals 100

You can see that 45 was added to 55 to make 100.

55 + 45 = 100

So we now know that 55 + 45 makes 100. If you adjust the numbers slightly, you can find other pairs that make 100.

Look at these.

51 + 49 = 100

52 + 48 = 100

53 + 47 = 100

54 + 46 = 100

55 + 45 = 100 (this is the calculation you worked out above)

56 + 44 = 100

57 + 43 = 100

58 + 42 = 100

59 + 41 = 100

Can you see a pattern in the ones?

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Example 5

What must I add to 37 to make 100?

Let鈥檚 use a part whole model to show this.

First, let鈥檚 make 37 and partition it into tens and ones.

part whole model showing 37 can be split into 2 parts: 3 and 7

How many do you need to add to 7 to make another multiple of 10?

You need 3, so let鈥檚 draw another part-whole model and write in 3.

part whole model showing 37 can be split into 2 parts: 3 and 7. another part whole with a part of 3

30 + 7 + 3 makes 40.

What do you need to add to 40 to make 100?

You will need 60.

part whole model showing 37 in 2 parts: 3 and 7. part whole showing a number is split into 3 and 60

What number do we write in the top part of the part whole model?

3 + 60 = 63

part whole model showing 37 and another showing 63

Now add up all the multiples of 10.

This shows that:

37 + 63 = 100

30 + 10 + 60 = 100

Another way to solve this would be to subtract 37 from 100.

Look at this 100 square, where 37 has been taken away from 100.

100 - 36 = 63 on a hundred square

The answer is 63.

100 - 37 = 63

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Activity 1

A girl thinking

Solve these questions using a number line, hundred square, known facts or a part-whole model.

  • 43 + ? = 100
  • 28 + ? = 100
  • 79 + ? = 100
A girl thinking
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Activity 2

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NEW! Play Guardians: Defenders of Mathematica - the winter update
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More on Adding and subtracting

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