Add and Subtract Fact Families
Fact families show how addition and subtraction work together.
What's 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.