Lesson 4

Measuring Mass

Est. Class Sessions: 2–3

Summarizing the Lesson

When students have completed the work on the Number Sentences pages, ask several volunteers to share their true number sentences for Question 1A, 4 × 5 + 2 × 10 = . Choose volunteers so that a variety of answers can be heard.

As each student writes his or her number sentence on chart paper, ask the class:

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  • Is this a true number sentence? (Possible response: No, 4 × 5 + 2 × 10 = 7 × 5 is not a true number sentence.)
  • Show or tell us how you know. (Possible response: I know because one side of the equal sign amounts to 40. 7 × 5 = 35. In order for it to be true, both sides of the equal sign must be the same amount. Also, when I place four 5-gram masses and two 10-gram masses in Pan 1 and seven 5-gram masses in Pan 2, the pans do not balance.)
  • Does anyone have another solution? (Possible response: Yes, I balanced the pans with eight 5-gram masses, 4 × 5 + 2 × 10 = 8 × 5.)

Repeat the questioning. Next, show a display of the chart on the Compare to 20 Grams Master. Ask students to list examples of items they measured in Question 4 that were less than, equal to, and greater than 20 grams. Classify the objects by recording them in one of the three columns. See Figure 2.

Assign the Balancing Masses pages in the Student Activity Book to students. These pages ask students to apply what they have learned about using the two-pan balance to solve problems that involve different standard masses. For each problem, students are to write number sentences to show their work.

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Use the Balancing Masses pages in the Student Activity Book to assess students' abilities to write number sentences to represent comparisons using the less than (<), greater than (>), or equal sign [E2] and solve multiplication problems involving mass [E3].

Student Guide:
Student Activity Book: 490 491
Answers
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SG_Mini
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SG_Mini
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Master:
Compare to 20 Grams chart
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