1. Understanding rounding to the nearest ten (C)

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: Round to the nearest hundred using a number line.

Students bring prior knowledge of place value from 2.MD.B.6. This prior knowledge is extended to rounding as students use number lines to determine what value to round to. A conceptual challenge students may encounter is identifying what benchmark numbers a value is between.

The concept is developed through work with a number line, which supports understanding of relational location of values as compared to benchmark numbers.

This work helps students deepen their understanding of number because students use place value knowledge and benchmark numbers (multiples of 10 and 100) on a number line to understand why numbers can be estimated or rounded to close numbers.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they find estimations of values through rounding using place value. A number line is created to quickly determine the estimation of a number based on its proximity to benchmark values.

Key vocabulary:

• benchmark number
• estimation
• rounding
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