Add and Subtract Fact Families
Fact families show how addition and subtraction work together.
What Is a Fact Family?
Three numbers can make a little family when they are related by addition and subtraction.
Once we know one fact in the family, we can find the others.
Example: 3, 5 and 8
3 + 5 = 8
5 + 3 = 8
8 − 3 = 5
8 − 5 = 3
Why They Are a Family
All the facts use the same three numbers.
Addition joins the smaller numbers to make the biggest number. Subtraction breaks the biggest number back into the smaller ones.
Another Family: 4, 6 and 10
4 + 6 = 10
6 + 4 = 10
10 − 4 = 6
10 − 6 = 4
Using Fact Families to Find Missing Numbers
Fact families are very helpful when a number is missing.
Example: 10 − = 6
In the family above, 10 − 4 = 6, so the missing number is 4.
Example: + 6 = 10
In the family above, 4 + 6 = 10, so the missing number is 4.
Try It Yourself
Look at this family:
Family: 2, 7 and 9
2 + 7 = 9
7 + 2 = 9
9 − 2 = 7
9 − 7 = 2
Can you find the missing number?
+ 2 = 9
Fact families help us see how addition and subtraction belong together.