Shapes and Their Perimeter

Lesson 5

Math

Unit 5

3rd Grade

Lesson 5 of 16

Objective


Understand perimeter to be the boundary around a two-dimensional shape. Compare perimeters of various polygons using concrete non-standard units.

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.

Criteria for Success


  1. Understand perimeter to be the boundary of a shape.
  2. Measure the perimeter of a polygon by outlining the polygon with unit lengths using concrete non-standard units (i.e., paper clips) and counting the units to find the total (MP.5). 
  3. Compare the perimeters of two polygons by comparing the number of paper clips used to trace the boundary of each polygon (MP.5).
  4. Distinguish between area and perimeter conceptually and visually, understanding the area to be the space a figure takes up and the perimeter to be the distance around a shape.
  5. See that two shapes can have the same area but different perimeters or the same perimeter and different areas (without formally computing both).

Tips for Teachers


Lesson Materials

  • Markers or crayons (2 per student) — Students could use a pen and a pencil instead
  • Paper clips (20 per student) — These should measure 1 inch in length. See Anchor Task 1 for more information, including how to modify materials for paper clips of a different length. Students will also need these for the Extra Practice Problems. Alternately, you can cut #4 from the Extra Practice Problems.
  • Square-sized paper (1 per student) — This should measure about 3" by 3". It is needed for the Problem Set.
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Anchor Tasks

25-30 minutes


Problem 1

Maureen wants to wrap ribbon around her mirror and around her picture frame. Will she need more ribbon for her mirror or her picture frame? Both are shown below.

Guiding Questions

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Student Response

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Problem 2

Outline both shapes below in one color. Then color the inside of both shapes in another color.

a.   Which color represents the perimeter of the shape? How do you know? What does the other color represent?

b.    Which shape has greater perimeter? How do you know?

c.   Which shape has greater area? How do you know?

Guiding Questions

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Student Response

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Problem Set

15-20 minutes


Discussion of Problem Set

  • Does the shape you drew in #1(a) have the same perimeter as the shape your partner drew for #1(a)? How do you know?
  • How is area different than perimeter? Why did the perimeter of the shape change but the area stayed the same?
  • Explain to a partner how you could use paper clips to figure out which shape has the greatest perimeter in #2. 

Target Task

5-10 minutes


a.   Color the inside of the following shape red. Color the outside edges of the shape blue. 

b.   Which color represents the perimeter of the shape? How do you know?

c.   Use paper clips to measure the perimeter of the shape. 

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 perimeter of polygons whose sides are marked with unit length marks by counting the unit lengths.

Lesson 6
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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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