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Parent guide · Grade 3 Math · Unit 7

Lesson 7.3 Perimeter

Written for the parent. Read the Say this lines aloud as they are, or in your own words. Answers for you are marked Listen for.

At a glance

Time
5 sessions of 25–30 minutes
Goal
Find perimeter and a missing side.
You need
  • Pencil and crayons
Print
Worksheet A · Worksheet B · the lesson page (it also has a short video (7:28))

Steps

  1. Do this: Ask these out loud. Your child answers out loud; no paper needed.

    • Ask: “10 × 9” Listen for: 90
    • Ask: “8 × 10” Listen for: 80
    • Ask: “3 × 9” Listen for: 27
    • Ask: “10 × 2” Listen for: 20
    • Ask: “10 × 10” Listen for: 100

  2. Say this: “Add all the side lengths. For a rectangle, 2 lengths and 2 widths.”

    Say this: “Perimeter is in units (feet), not square units.”

    Say this: “Perimeter: the distance all the way around a shape.”

  3. Show: A field has sides of 4, 12, 3, 10 and 3 m. How much fence goes all the way around?

    Say this: “4 + 12 + 3 + 10 + 3 = 32”

    Say this: “Perimeter = 32 m”

    Answer: 32 m

    Show: A rectangular pen has a perimeter of 14 ft. Its length is 4 ft. What is its width?

    Say this: “The two lengths: 2 × 4 = 8”

    Say this: “14 − 8 = 6 for the two widths”

    Say this: “6 ÷ 2 = 3”

    Answer: 3 ft

  4. Do this: Your child does these with you. Let them try first; help only after a real try.

    Ask: Find the perimeter of a rectangle 9 ft long and 8 ft wide.

    rectangle

    Listen for: 34 ft

    If stuck: Add all four sides: 9 + 8 + 9 + 8 = 34

    Ask: Find the perimeter of a rectangle 9 ft long and 5 ft wide.

    rectangle

    Listen for: 28 ft

    If stuck: Add all four sides: 9 + 5 + 9 + 5 = 28

    Ask: Find the perimeter of a rectangle 8 ft long and 4 ft wide.

    rectangle

    Listen for: 24 ft

    If stuck: Add all four sides: 8 + 4 + 8 + 4 = 24

    10 more practice items on the lesson page, and on Worksheet A and Worksheet B.

    • Mixing up area and perimeter.

  6. On graph paper, design a garden bed with an area of 24 squares. How many different rectangles can you make? Which has the shortest fence (perimeter)?

  7. Say this: “Tell me what you learned today. Show me with your hands or the counters if you like.”

    Listen for: Find perimeter and a missing side.

  8. Fact drill. Square numbers: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100.

Spread over the week

5 sessions of 25–30 minutes. Stop while it is still going well.

  1. Session 1. Warm-up, then teach the new idea (steps 1 and 2).
  2. Session 2. Warm-up again, then show how with the examples.
  3. Session 3. Practice together, then play the game.
  4. Session 4. More practice on the worksheet, and the daily habit.
  5. Session 5. Quick check: narration and a few practice items. Move on when it is mostly right.