Lesson 5

Addition with Larger Numbers

Est. Class Sessions: 4

Developing the Lesson

Part 1. Reviewing Addition Strategies

Choose a Mental Math Strategy. Display the Addition Strategies Menu Master from Lesson 4 and ask students to look at their copies of the same menu. Remind students that the menu features strategies for adding 2-digit numbers.

Ask:

X
  • Which strategy do you like to use the most? Why?
  • Which strategy is the hardest to use? Why?
  • Which strategies require paper and pencil? (Possible response: Compact Method, All-Partials, Expanded Form)
  • Which strategies help you to solve problems in your head? (Possible response: Counting On, Finding Friendly Numbers)

Display the following addition problems. Ask students to first talk with a partner about how they would solve them:

26 + 30      88 + 96      298 + 3

Have students solve the problems using any strategy they choose. Expect students to choose different strategies to solve the same problem. See Figure 1. The question is not “Which strategy is the right strategy to solve this problem?” Any strategy could be applied to the solution of any problem. Instead, the question revolves around which strategy helps students solve the problem in an efficient manner.

Ask:

X
  • Who used a mental math strategy to solve this problem? Why?
  • Who used a paper-and-pencil strategy to solve this problem? Why?
  • Which of these problems is the hardest to do in your head? Why? (Possible response: 88 + 96 because there are trades and it is hard to remember the numbers in my head.)
  • Which of these problems is the easiest to do in your head? Why? (Possible response: For 298 + 3, I count on 3 from 298 to 301.)

Show students the example given in Figure 1.

Say:

X
  • Both of these strategies can be used to solve 298 + 3. Which can be done more quickly or in the fewest steps? (the mental math strategy)
  • When does it make sense to use a mental math strategy?

Mental math may be quicker to use than paper and pencil. Students may respond that they choose mental math strategies when the numbers are easy to see and use in their heads. For example, numbers with zeros are easier to add mentally. On the other hand, problems that involve trades may be easier with paper and pencil, as will problems that involve multidigit numbers or problems with many addends. Stress that it is important to choose a quick and efficient way to solve a problem. An efficient strategy reaches the correct answer, fits the problem, can be done in a few steps, can be done quickly, and is easy to understand.

X

In Lesson 4, students made and looked at an Addition Strategies Menu. The examples all involved two-digit numbers. In this lesson, students use the same menu structure to include examples for 3- and 4-digit numbers. The menus are the same except for the examples.

Revise Addition Strategies Menu. Tell students they will extend their study of addition problems involving three- and four-digit numbers. Direct student's attention back to the Addition Strategies Menu from Lesson 4. See Figure 2.

Ask:

X
  • Look at the strategies we used to add 2-digit numbers. What should we change on this menu so we can use it to help us add 3- and 4-digit numbers?

Distribute a copy of the My Addition Strategies Menu for Larger Numbers Master to each pair of students. Ask students to make a new addition strategies menu for larger numbers by changing the examples to ones that will help them add 3- and 4-digit numbers. While students are working, circulate and select students to display an example for each strategy. Ask students to record these examples on a display copy of the My Addition Strategies Menu Master or on chart paper. These will be used for reference during class discussion.

Compare the Menus. Now display and direct students' attention to the Addition Strategies Menu page in the Student Guide Reference section. See Figure 3. Compare the menus.

Ask:

X
  • What is the same about the menus? (Possible response: They all help solve addition problems, and include mental math strategies and paper-and-pencil strategies. The strategies are the same on both menus.)
  • What is different about these menus? (Possible response: The new menu uses larger numbers in the problems.)
  • Are the strategies for adding 3- and 4-digit numbers very different from those we used to add 2-digit numbers? (No. There may be more trades, but the strategies are the same.)
Student Guide:
Student Activity Book:
Master:
Different strategies to solve 298 + 3
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Addition Strategies Menu for adding 2-digit numbers from Lesson 4
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Addition Strategies Menu from Student Guide Reference
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