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Year 4 Maths — 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.Every side of every shape here is 6 centimetres long. Match each regular shape to its perimeter.

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

  2. 2.Every length here is in centimetres. Which shape has the largest perimeter?

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

  3. 3.A four-sided shape has sides of 3 cm, 7 cm, 4 cm and 9 cm. What is its perimeter, in centimetres? Give just the number.

  4. 4.A regular hexagon has sides of 5 cm. What is its perimeter, in centimetres? Give just the number.

  5. 5.Every length here is in centimetres. Sort each shape by whether its perimeter is below 30 or above 30.

    Groups: Perimeter below 30 · Perimeter above 30

    • A rectangle 10 by 4
    • A regular pentagon of side 7
    • A regular hexagon of side 6
    • A rectangle 9 by 7
    • A triangle with sides 8, 9 and 10
    • A square of side 6

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

  7. 7.A triangle has a perimeter of 24 cm. Two of its sides are 9 cm and 7 cm. How long is the third side, in centimetres? Give just the number.

  8. 8.A triangle has sides of 6 cm, 8 cm and 5 cm. What is its perimeter, in centimetres? Give just the number.

Answer key — Year 4 Maths — Perimeter: once round the outside

  1. 1. Triangle → 18; Square → 24; Pentagon → 30; Hexagon → 36; Octagon → 48
  2. 2. b) A regular pentagon of side 5
  3. 3. 23
  4. 4. 30
  5. 5. A square of side 6 → Perimeter below 30; A rectangle 10 by 4 → Perimeter below 30; A rectangle 9 by 7 → Perimeter above 30; A regular pentagon of side 7 → Perimeter above 30; A triangle with sides 8, 9 and 10 → Perimeter below 30; A regular hexagon of side 6 → Perimeter above 30
  6. 6. 8
  7. 7. 8
  8. 8. 19