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Solve.

SCHOOL STORE The school store sold 22 pencils on Tuesday, 31 pencils on Wednesday, and 19 pencils on Thursday. How many pencils did the school store sell in all? Explain your reasoning.

Understand Read the problem. Write what you know.

The number of pencils sold was 22, 31, and 19.

In this problem, the words “in all” mean to add.

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Plan Pick a strategy. One strategy is to solve a simpler problem.

Look for two numbers that will have a sum with a 0 in the ones place. Add those numbers together first.

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Solve Write an expression for how many pencils the school store sold in all.

22 + 31 + 19

Use the Associative Property of Addition to rewrite the expression so that it is easier to simplify mentally. Then find the sum.

22 + 31 + 19 = 22 + (31 + 19)

= 22 + 50

= 72

The school store sold 72 pencils in all.

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Check Work backward to check your answer.

72 – 22 – 31 – 19 = 0