# 12. Find the missing side of a rectangle (FP)

teaches Common Core State Standards CCSS.Math.Content.4.MD.A.3 http://corestandards.org/Math/Content/4/MD/A/3
teaches Common Core State Standards CCSS.Math.Content.4.NBT.B.6 http://corestandards.org/Math/Content/4/NBT/B/6
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8

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Lesson objective: Divide to find the measure of an unknown side of a rectangle.

This lesson helps to build fluency with whole number division. Partial quotients is used here because it further develops a strategy for solving division problems when the equations can't be solved mentally. This work develops students' understanding that the relationship between multiplication and division can be used to solve real-world problems.

Students engage in Mathematical Practice 8 (look for and express regularity in repeated reasoning) as they utilize the multiplication formula used to find area by dividing to solve for a missing side.

Key vocabulary:

• area
• inverse

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