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lesson 29
1 hour

Estimate Sums And Differences


Description

Objective:  Estimate sums and differences using benchmark numbers.

Lesson 29 focuses on the process of using benchmark numbers to estimate sums and differences of mixed numbers. Students once again call on their understanding of benchmark fractions as they determine, prior to performing the actual operation, what a reasonable outcome will be. One student might use benchmark whole numbers and reason, for example, that the difference between 4 1/5 and 1 3/4 is close to 2 because 4 1/5 is closer to 4 than 5, 1 3/4 is closer to 2 than 1, and the difference between 4 and 2 is 2. Another student might use familiar benchmark fractions and reason that the answer will be closer to 2 1/2 since 4 1/5 is about 1/4 more than 4 and 1 3/4 is about 1/4 less than 2, making the difference about a half more than 2, or 2 1/2 .

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Credits

From EngageNY.org of the New York State Education Department. Grade 4 Mathematics Module 5, Topic F, Lesson 29. Available from engageny.org/resource/grade-4-mathematics-module-5-topic-f-lesson-29; accessed 2015-05-29.
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