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Grade 3 Math — Perimeter: once round the outside

Find the perimeter of any straight-sided shape by adding the lengths of its sides, and work backwards to a missing side.

Name: ________________________

Before you start

An L-shaped garden, with every side drawn as its own strip. Find all of them, and count how many there are.

123456
  1. 1. The top side
  2. 2. The short side going down
  3. 3. The step across
  4. 4. The long side going down
  5. 5. The bottom side
  6. 6. The tall side up the left

Six sides, not four — the step in the middle adds two more, and leaving one of those out is the commonest way a perimeter goes wrong.

  1. 1.A square has sides of 9 inches. What is its perimeter, in inches? Give just the number.

  2. 2.Every side of every shape here is 6 inches long. Match each regular shape to its perimeter.

    • Triangle
    • Square
    • Pentagon
    • Hexagon
    • Octagon
    • 36
    • 30
    • 24
    • 48
    • 18

  3. 3.A square has a perimeter of 32 inches. How long is each side, in inches? Give just the number.

  4. 4.A regular octagon has a perimeter of 56 inches. How long is each side, in inches? Give just the number.

  5. 5.A path goes right round a rectangular lawn 15 ft long and 10 ft wide. How far is it once round, in feet? Give just the number.

  6. 6.A rectangle is 12 inches long and 7 inches wide. What is its perimeter, in inches? Give just the number.

  7. 7.Every length here is in inches. Put these shapes in order by perimeter, smallest first.

    • A square of side 8
    • A rectangle 5 by 4
    • A regular hexagon of side 4
    • A square of side 3
    • A square of side 4

  8. 8.Every length here is in inches. Which shape has the largest perimeter?

    • a) A rectangle 8 by 3
    • b) A square of side 6
    • c) A regular pentagon of side 5
    • d) A triangle with sides 7, 7 and 7

Answer key — Grade 3 Math — Perimeter: once round the outside

  1. 1. 36
  2. 2. Triangle → 18; Square → 24; Pentagon → 30; Hexagon → 36; Octagon → 48
  3. 3. 8
  4. 4. 7
  5. 5. 50
  6. 6. 38
  7. 7. 1. A square of side 3 2. A square of side 4 3. A rectangle 5 by 4 4. A regular hexagon of side 4 5. A square of side 8
  8. 8. c) A regular pentagon of side 5