# 5. Determining accuracy in rounding to the nearest ten or hundred (A)

teaches Common Core State Standards CCSS.Math.Content.3.NBT.A.1 http://corestandards.org/Math/Content/3/NBT/A/1
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8

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Lesson objective: Apply understanding of estimation to determining reasonability of sums and differences in real-world contexts.

This lesson provides an opportunity for students to apply their knowledge and understanding of estimation to a real-life situation. Students are asked to use an estimate to determine which truck to use to minimize expenses, but still carry all of the required weight.

Key Concept students will use:

• Rounding is based on place value and may be used to gauge the reasonableness of calculations or may be used in place of a specific calculation.

Skills students will use:

• Represent whole numbers on a number line diagram with equally spaced points and recognize the distance and proximity from other numbers (Grade 2, Unit 3)
• Use a number line to determine which benchmark values are close and can be used as an estimate
• Determine reasonableness of a sum or difference based on the real-life scenario

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they use their knowledge of rounding and apply it to a new situation. They determine estimates and reasonability of calculations with sums and differences.

Key vocabulary:

• estimate
• overestimate
• reasonable
• underestimate
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