# 12. Find the perimeter of polygons marked with unit length markers (FP)

teaches Common Core State Standards CCSS.Math.Content.3.MD.D.8 http://corestandards.org/Math/Content/3/MD/D/8
teaches Common Core State Standards CCSS.Math.Practice.MP5 http://corestandards.org/Math/Practice/MP5

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Lesson objective: Find the perimeter of a polygon marked with unit length markers, but without numbers.

This lesson helps to build procedural skill with determining perimeter. Polygon models are used here because they provide a visual that supports the skill of finding perimeter. This work develops students' understanding that perimeter is the sum of the length of the sides of a polygon.

Students engage in Mathematical Practice 5 (Use appropropriate tools strategically) as they use unit length markers to determine perimeter in the same way they would use a ruler. They can also use other length measuring tools but without numbers marking the units.

Key vocabulary:

• perimeter
• polygon
• sides
• unit

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