# 4. Extend understanding of addition and subtraction strategies using number lines (C)

teaches Common Core State Standards CCSS.Math.Content.2.NBT.B.5 http://corestandards.org/Math/Content/2/NBT/B/5
teaches Common Core State Standards CCSS.Math.Practice.MP1 http://corestandards.org/Math/Practice/MP1

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Lesson objective: Extend understanding that addition and subtraction can be used in different ways.

Students bring prior knowledge of addition and subtraction from 2.OA.1. This prior knowledge is extended to include an understanding of more ways addition and subtraction can be used as students use strategies that they are comfortable with (such as number lines) to solve addition and subtraction problems. A conceptual challenge students may encounter is believing addition and subtraction can only be used one way (i.e., put together, take away).

The concept is developed through work with a number line, which shows that there are many addition and subtraction strategies that can be used to solve the same problem.

This work helps students deepen their understanding of number because there are many different situations when you can add and subtract numbers to get the answer you are looking for.

Students engage in Mathematical Practice 1 (Understand problems and perservere in solving them) as they use a number line to add and subtract.

Key vocabulary:

• subtraction
• number line

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