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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
