Lesson 7

Adding and Subtracting Multiples of Ten

Est. Class Sessions: 2

Summarizing the Lesson

Display the Maria's Marble Mart Master and pose this problem for students:

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  • Joe wants to buy 60 marbles. He can buy bags of 10, 20, or 30 marbles. Name the different ways that his order can be filled.

Have students work in pairs to find combinations of the three kinds of bags and write number sentences for their solutions. See Figure 4.

When student pairs finish, have them share their solutions and demonstrate how they count the tens in their answer. Write the different combinations of tens on chart paper or another display.

Some partitions of 60 using the bags of 10, 20, or 30 marbles are as follows:

  • 30 + 30 = 60
  • 30 + 20 + 10 = 60
  • 20 + 20 + 20 = 60
  • 10 + 10 + 10 + 10 + 20 = 60
  • 10 + 10 + 10 + 10 + 10 + 10 = 60

Introduce the next problem on the Maria's Marble Mart Master to review money concepts:

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At Maria's Marble Mart, a bag of 10 marbles costs 10¢, a bag of 20 marbles costs 20¢, and a bag of 30 marbles costs 30¢. Tonya wants to buy 60 marbles. She buys one of each size bag: a 10-marble bag, a 20-marble bag, and a 30-marble bag.

  • How much money will she pay for her marbles? (60¢)
  • What is the number sentence?
    (30¢ + 20¢ + 10¢ = 60¢)
  • What coins can she use to pay Maria? Include a number sentence. (Possible response: 2 quarters and 1 dime. 25¢ + 25¢ + 10¢ = 60¢.)
  • What are some other combinations of coins? (Possible response: 6 dimes or 1 quarter, 1 nickel, and
    3 dimes)

Have students share different combinations of coins and record them on chart paper or a display. Have students demonstrate how they count the coins in their answers.

Ask students to return to the first problem and determine whether the new configuration of bags will cost the same as buying one of each kind of bag. For example, if their solution was 2 bags of 20 and 2 bags of 10, it will cost 20¢ + 20¢ + 10¢ + 10¢ + 60¢.

Assign the Maria's Bags of Marbles pages in the Student Activity Book to assess students' abilities to solve addition and subtraction problems using multiples of ten.

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Use the Maria's Bags of Marbles pages in the Student Activity Book to assess students' abilities to represent partitions of numbers using number sentences [E2]; represent addition and subtraction using number sentences [E3]; and solve addition and subtraction problems involving multiples of ten [E7].

Adventure Book:
Student Activity Book: 353 354
Answers
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SAB_Mini
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SAB_Mini
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Master:
One possible partition of 60
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