Lesson 9

Fact Families

Est. Class Sessions: 1

Summarizing the Lesson

Choose one or two students to present one of the addition facts in their fact families, including one number sentence that includes a 0 such as 0 + 3. Ask the other students to use tools such as cubes, number lines, ten frames, and part-whole diagrams to find the related number sentences in the fact family. Record the number sentences as they are generated. Selected students can verify the number sentences.

See the Sample Dialog.

Ask:

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  • What is the turn-around fact for this addition sentence?
  • How are these subtraction sentences related?
  • If you know this addition fact, how can you find a related subtraction fact?
  • How do you know that these number sentences belong in the same fact family?

Display the following fact family and encourage students to use tools to complete the first addition number sentence:

2 + 3 =
3 + = 5
5 − 2 =
5 − = 2

Use tools and work through the problems together.

Ask:

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  • How does knowing 2 + 3 = 5 help you solve 3 plus another number equals 5? (Possible response: The turn-around fact for 2 + 3 = 5 is 3 + 2 = 5.)
  • Is there another way to solve this problem? (Possible response: I know I need to add some number to get to 5 so I start at 3 and count up to 5. I count up 2 times so I know 2 is the missing number. See Figure 3.)
  • How does knowing 3 + 2 = 5 help you solve 5 − 2? (Possible response: If I have 3 cubes and add 2 more cubes, I have 5 cubes. So if I start with 5 cubes and take 2 cubes away, I have 3 cubes left.)
  • 5 is the whole, and I take some away and have 2 left. How many did I take away? (3)
  • Can you turn around 5 − 2 = 3? Does 2 + 5 = 3? Show us with cubes. (No. I can take 2 cubes from 5 cubes, but can't take 5 cubes from 2 cubes.)
  • How are 2, 3, and 5 related? (I can use them to make 2 addition fact sentences and 2 subtraction fact sentences, a fact family.)
  • Think about the numbers 1, 2, and 5. Are these numbers related to a fact family? Explain how you know. (No; when you add 1 + 2 or 2 + 1, the number is 3, not 5.)

Assign the Fact Families Practice page in the Student Activity Book to individual students.

X

Use the Fact Families Practice pages in the Student Activity Book to assess students' abilities to find the related subtraction sentence for an addition sentence (e.g., fact families) [E3] and find the unknown whole number in an addition or subtraction equation relating three whole
numbers [E5].

Adventure Book:
Student Activity Book: 163 164
Answers
X
SAB_Mini
+
X
SAB_Mini
+
Master:
Solve 3 + = 5 by counting up on the number line
X
+