Look at this number square, which shows all the bonds you should know by heart up to 20.

You can use this table to work out additions and subtractions right up to 100.

**Example 1**

Add 36 + 9

**Answer**

We split 36 into 30 **and** 6.

We now need to work out

30 + 6 + 9

You should know this by heart, but the number square shows that

6 + 9 = 15

So

36 + 9 = 30 + 6 + 9

= 30 + 15 = **45**

**Example 2**

Subtract 25 - 9

**Answer**

We split 25 into 10 **and** 15.

We now need to work out

10 + 15 - 9

You should know this by heart, but the number square shows that

15 - 9 = 6

When you subtract, the **starting **number is **inside **the square.

So

25 - 9 = 10 + 15 - 9

= 10 + 6 = **16**