Unit 2 Contents

Fact Families

John and Suzanne noticed that the addition fact 9 + 6 = 15 is related to the subtraction facts 15 − 6 = 9 and 15 − 9 = 6.

“These facts all use 6, 9, and 15. There are a lot of facts that use the same numbers,” said John. The set of math facts you can make from the same numbers is called a fact family.

John decided to list the number sentences in the fact family for another set of numbers: 6, 7, 13. “The easiest for me is addition. I add the two smaller numbers to get the largest,” he said. Then he wrote:

“Once I know one addition sentence, the other is easy, since you can turn the numbers around and get the same answer.”

“To get the subtraction facts in this fact family, I start with the largest number, which is 13. Then I think about 6 and 7. If I take one of the numbers away from 13, I get the other. This gives me two subtraction sentences.”

He wrote:

“It helps me remember them when I think of these facts together.”

Check-In: Questions 12–13

1. Write the number sentences in the fact family for the numbers 4, 9, 13.
2. Show or tell what strategy you can use to solve each number sentence.
1. Write the number sentences in the fact family for the numbers 7, 9, 16.
2. Show or tell what strategy you can use to solve each number sentence.