Understanding Fact Families

A fact family is a group of three numbers that work together to make four different math facts. Just like people in a family are related to each other, these numbers are related through addition and subtraction.

How Fact Families Work

Let's look at a fact family made of the numbers 3, 5, and 8.

With these three numbers, we can write two addition sentences and two subtraction sentences.

Addition Facts (joining the small numbers): When you add the two smaller numbers together, you get the biggest number.

$3 + 5 = 8$
$5 + 3 = 8$

Subtraction Facts (taking away from the big number): When you start with the biggest number and subtract one of the smaller numbers, you get the other smaller number.

$8 - 3 = 5$
$8 - 5 = 3$

These four math sentences make up the complete fact family!

Why Are Fact Families Important?

Fact families teach us that addition and subtraction are connected. They are opposites!

If you know an addition fact, you can easily figure out the subtraction fact. For example, if you know that $6 + 4 = 10$ , you don't even need to count to solve $10 - 4 = ?$ because you know the missing family member is $6$ !