Shapes and Their Perimeter

Lesson 12

Math

Unit 5

3rd Grade

Lesson 12 of 16

Objective


Solve more complex word problems involving perimeter, such as finding a missing side length given perimeter and other side lengths.

Common Core Standards


Core Standards

  • 3.MD.D.8 — Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.

Foundational Standards

  • 3.OA.D.8

Criteria for Success


  1. Solve word problems involving perimeter, including given the perimeter of a regular polygon, find its side length and given the perimeter of a rectangle and of its dimensions, find the other dimension (MP.4).
  2. Write an equation to represent the perimeter of a shape (including simplified equations, such as a multiplication equation for a regular polygon) (MP.2).
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Anchor Tasks

25-30 minutes


Problem 1

Gabrielle put a frame around a clock that is in the shape of a regular hexagon. If Gabrielle used 42 centimeters of framing, how long is each side of the clock?

Guiding Questions

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Student Response

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Problem 2

The perimeter of a rectangular index card is 26 inches. Its length is 5 inches. What is its width?

Guiding Questions

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Student Response

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Problem Set

15-20 minutes


Discussion of Problem Set

  • How did knowing the perimeter and the width help you find the length of the rectangle in #2?
  • How did you find the lengths of the sides of the rug in #3?
  • Which problem did you find most difficult? Why?

Target Task

5-10 minutes


Problem 1

A rectangular notecard has a perimeter of 20 inches. The length of the notecard is 4 inches. What is the width of the notecard?

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Student Response

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Problem 2

A square has a perimeter of 12 centimeters. What are the side lengths of the square?

Student Response

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Additional Practice


The Extra Practice Problems can be used as additional practice for homework, during an intervention block, etc. Daily Word Problems and Fluency Activities are aligned to the content of the unit but not necessarily to the lesson objective, therefore feel free to use them anytime during your school day.

Word Problems and Fluency Activities

Word Problems and Fluency Activities

Help students strengthen their application and fluency skills with daily word problem practice and content-aligned fluency activities.

Next

Find rectangles with the same area and different perimeters.

Lesson 13
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Lesson Map

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Topic A: Attributes of Two-Dimensional Shapes

Topic B: Understanding Perimeter

Topic C: Distinguishing Between Area and Perimeter

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