# 5. Conversions with Customary Measurement - Double Number Line (C)

teaches Common Core State Standards CCSS.Math.Content.4.MD.A.1 http://corestandards.org/Math/Content/4/MD/A/1
teaches Common Core State Standards CCSS.Math.Content.4.OA.A.1 http://corestandards.org/Math/Content/4/OA/A/1
teaches Common Core State Standards CCSS.Math.Practice.MP2 http://corestandards.org/Math/Practice/MP2
teaches Common Core State Standards CCSS.Math.Practice.MP4 http://corestandards.org/Math/Practice/MP4

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Lesson objective: Understand that larger units of customary measurement can be converted to smaller units with multiplication.

Students bring prior knowledge of measurement from 2.MD.A.1. This prior knowledge is extended to converting units of length from feet to inches as students create double number lines to show equivalency. A conceptual challenge students may encounter is conversions of measurement as multiplicative, not additive.

The concept is developed through work with the double number line, which shows how two different units of measure can represent the same quantity.

This work helps students deepen their understanding of equivalence because they can see that 6 feet is equivalent to 72 inches.

Students engage in Mathematical Practice 4 as they create double number lines that represent the relationship between the number of feet and the number of inches.

Key vocabulary:

• customary unit of measure
• double number line
• feet
• inch
• length
• yard
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