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This activity is all about families.
No, not that sort of family - maths families!
Addition and subtraction family facts normally come in fours.
There are two addition facts and two subtraction facts.
If we know just one of them, we can always work out the other three.
If we know the addition fact that
23 + 35 = 58
we can say that the other addition fact in this family is
35 + 23 = 58
The subtraction facts in this family will be
58 - 35 = 23
and
58 - 23 = 35
Got that?
Example
Use the addition fact:
15 + 18 = 33
to work out the missing number below:
33 - 
= 15
Answer
15 + 18 = 33
So 33 - 18 = 15 and 33 - 15 = 18
The missing number is 18.
33 - 18 = 15
Remember that if you know just one of the family facts, you can work out all the other three.
Let's have a go at some questions now.
