Lesson 5

Model Repeated Addition and Subtraction

Est. Class Sessions: 2–3

Developing the Lesson

Part 1: Use Addition Strategies to Solve a Multiplication Problem

Display and read the Ducks in Boots page aloud as students follow along in the Student Activity Book. Ask students to estimate how many boots the ducks will need. Ask students to look at their number lines and tell which interval (as discussed in Lesson 3) they think the answer will be in and give their reasons.

Ask:

X
  • How many ducks are there? (13)
  • How many boots will each duck need? (2)
  • Look at your number line. What interval do you think the answer will be in? Between 0–10? 11–20? 21–30? (21–30)
  • Why do you think so? (Responses will vary. Possible response: 13 is close to 10 and 10 + 10 = 20. I think the answer is close to 20.)

Without discussing specific strategies, have students complete the Ducks in Boots page. Ask them to draw a picture and explain their strategy in words and numbers. Have connecting cubes, number lines, and 100 Chart readily available. Circulate around the room and note if there are students who are counting all to find the answer. Suggest to them that there is a way to find the solution more quickly.

Upon completion, ask students to share strategies. Encourage them to use the number line to demonstrate.

Ask:

X
  • How did you find how many boots were needed for 13 ducks? (Possible response: I used the number line and skip counted by twos 13 times: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26.)
  • Is there another strategy? Explain. (Possible response: I doubled 13. 13 + 13 = 26.)

Use Sample Dialog 1 to guide the discussion of strategies.

X

Use this Sample Dialog to discuss students strategies for solving the Ducks in Boots problem.

Teacher: What is your answer and how did you solve the problem?

Daniel: I used cubes and I made 13 groups of 2. Then I counted all of them and I got 26.

Teacher: You got the correct answer, Daniel, but is there a faster way to solve the problem?

Ana: I drew 13 ducks and each one had 2 boots, so I skip counted by 2s 13 times. I got 26 boots.

Teacher: That's a great way to solve the problem! Each duck needed the same number of boots, so skip counting by 2s is a good way to find the answer. Did someone solve it a different way?

Miguel: I wrote a number sentence: 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 = 26. I made sure I had 13 twos and then I skip counted by 2. I guess that's like Ana's strategy.

Teacher: That is very similar to Ana's but you wrote the number sentence instead of drawing a picture. Good answer, Miguel! Who else had a different strategy?

Jason: I doubled 13 and wrote 13 + 13 = 26. I knew that there were 13 ducks and if they each need 2 boots, that's 13 and 13.

Teacher: That's very good thinking, Jason. How did you find the answer to 13 + 13?

Jason: I did it on the number line. To add 13 + 13, I made 2 big jumps of 10 and 2 small jumps of 3 and I got 26.

Teacher: Great job! Some of you skip counted by 2s
13 times, and some of you doubled the number 13, but you still got 26 for an answer.

Adventure Book:
Student Activity Book: 475
Answers
X
SAB_Mini
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Master: