# Multiples of 10

### In this lesson:

• Why numbers like 10, 20, 30… are very useful
• How to use these numbers in addition
• Reversing the order of numbers

## Number Pairs

It is important to know the five pairs of numbers that add up to 10. These are:

1 + 9 = 10

2 + 8 = 10

3 + 7 = 10

4 + 6 = 10

5 + 5 = 10

## Multiples of Ten

Numbers like 10, 20, 30, 40 and so on, are very useful.

We call the numbers 10, 20, 30, 40, 50… multiples of 10, because they start at 10 and go up in 10s.

Now think of the number 39.

You can see that 39 is close to 40 and is 1 short of 40.

And you can also see that 58 is close to 60 and is 2 short of 60.

This makes it easier to work with numbers, adding and subtracting them.

## Addition in Action

Suppose you want 38 + 5.

You know that 38 is close to 40 and is 2 below it.

So take 2 of the 5 to make up to 40 and you have 3 more to add on, which gives 43.

So 38 + 5 = 43.

## Order of Addition

Notice also that if you wanted, say 5 + 77, you could add 5 to 77 because 5 + 77 will give the same answer as 77 + 5.

The order the numbers are in doesnâ€™t matter, you can always reverse the order if you want to.

So 5 + 77 = 82.