Lesson 4

Addition Review

Est. Class Sessions: 2–3

Developing the Lesson

Part 2. Adding with Mental Math Strategies

Mental Math Strategies. While using base-ten pieces and the base-ten recording sheet is helpful, stress that there may be other, simpler ways of finding solutions. It is important to find a quick and efficient way to solve problems. Direct students' attention to the Mental Math Strategies section of Addition Review in the Student Guide. Read the vignette together in which Jason and Rosa use mental math to solve 53 + 25 and discuss Questions 1–3. Students should see that using mental math to solve 53 + 25 is a quick way to solve the problem. Some may say that the numbers are easy to “see” and use in your head.

Direct students' attention to Question 4 and say:

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  • Look carefully at the problems in Question 4. Do not solve them yet, but instead talk with a partner. Can you use mental math to solve them or would you need paper and pencil to solve some?

Write the problems from Question 4 on the board or on chart paper. See Figure 3. Ask students to solve the problems. Have base-ten pieces available. As they complete the problems, choose some students to share their strategies with the class and have them record their solutions on chart paper, adding to the collection of strategies. Label them simply with the student's name such as “Linda's Strategy.” Identify a mental math strategy with a cloud or a thought bubble.

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When working with base-ten pieces at this point, it will be natural for students to start with the tens, since they read from left to right. Students can work in either direction when using base-ten pieces or using the all-partials method. See Figure 11 in this lesson and Paper-and-Pencil Method in the Background. However, when using the standard algorithm, it will be helpful for students to start with the ones digits. It is important to allow students to work with the pieces in ways that make sense to them. See the Background for a summary of the methods presented in this unit.

Ask the selected students to share the solutions they recorded:

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  • How did you solve 53 + 25?
  • Explain your solution strategy for 69 + 20. (Possible strategy: I found a number that was easier to add in my head than the 69 in 69 + 20. 70 + 20 = 90 and then I took 1 away to make 89.)
  • Did anyone use mental math to solve 22 + 74? (Possible strategy: I thought of 74 as 7 skinnies and 4 bits. I thought of 22 as 2 skinnies and 2 bits. In my head, I put the skinnies together to make 90 and the bits together to make 6, 96.)

Lead a class discussion about other strategies used to solve the problems. Record and post the solutions for use later in this lesson.

Student Guide: 136
Answers
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SG_Mini
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Student Activity Book:
Master:
Problems without trading from Question 4
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