Addition and Subtraction are closely linked.
From any addition fact, we can normally also get two subtraction facts.
Look at the addition fact:
3 + 5 = 8.
From this we can get the two subtraction facts:
8 - 5 = 3
8 - 3 = 5
This works with all numbers, even bigger ones.
Example
Complete the two subtraction facts from the following addition fact, to work out the values of A and B.
21 + 68 = 89
89 - 68 = A
89 - 21 = B
Answer
Look at the addition fact:
21 + 68 = 89.
From this we can get the two subtraction facts:
89 - 68 = 21
89 - 21 = 68
So we have shown that:
A = 21
B = 68