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Checking and securing understanding of perimeter for compound shapes

Lesson details

Learning outcome

I can calculate the perimeter of compound shapes made from rectangles, triangles, parallelograms and trapeziums efficiently.

Key learning points

  1. Before calculating perimeter, consider the shape and check you know the required lengths.
  2. It is not necessary to know every side length.
  3. Sometimes you can deduce the sum of a subset of side lengths.
  4. Identifying where you can be more efficient can make calculations simpler.

Keywords

  • Perimeter - The perimeter is the distance around a 2D shape.

  • Compound shapes - A compound shape is a shape created using two or more basic shapes.

  • Composite shapes - A composite shape is an alternative for a compound shape.

Common misconception

Pupils may miss an edge when calculating the perimeter.

Encourage the pupils to trace the perimeter to check that all edges have been included in the sum.

Teacher tip

This lesson involves Pythagoras' theorem and properties of shape, so you may wish to set a homework revisiting these skills in preparation for the lesson.

Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0
except where otherwise stated. See Oak's terms & conditions
(Collection 2).

Lesson video

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Prior knowledge starter quiz

6 Questions

Q1.
The __________ is the distance around a 2D shape.

area
Correct answer: perimeter
volume

Q2.
The perimeter of this rectangle is cm.

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Correct Answer: 14, fourteen, 14 cm, 14cm

Q3.
The perimeter of this parallelogram is cm.

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Correct Answer: 16.6, 16.6 cm, 16.6cm

Q4.
The perimeter of this triangle is cm.

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Correct Answer: 45, forty five, 45 cm, 45cm

Q5.
Which of these shapes has different perimeter to the other three shapes?

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An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz

Q6.
The length of the edge marked 'a' is cm.

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Correct Answer: 1.5, one and a half, 1.5 cm, 1.5cm

6 Questions

Q1.
Which of the following are examples of compound shapes?

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Correct Answer: An image in a quiz
An image in a quiz
An image in a quiz
Correct Answer: An image in a quiz
An image in a quiz

Q2.
The perimeter of this compound shape is cm.

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Correct Answer: 33, thirty three, 33 cm, 33cm

Q3.
The perimeter of this compound shape is cm.

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Correct Answer: 28, twenty eight, 28 cm, 28cm

Q4.
The perimeter of this compound shape is cm.

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Correct Answer: 64.4

Q5.
Match the marked edges with the correct calculations.

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Correct Answer:$$a$$,$$4 + c$$

$$4 + c$$

Correct Answer:$$b$$,$$8 − 3$$

$$8 − 3$$

Correct Answer:$$c$$,$$\sqrt{5^2-3^2}$$

$$\sqrt{5^2-3^2}$$

Correct Answer:$$d$$,$$\sqrt{\text{b}^2+12^2}$$

$$\sqrt{\text{b}^2+12^2}$$

Q6.
The perimeter of this compound shape is cm.

An image in a quiz
Correct Answer: 56, fifty six, 56 cm, 56cm

To help you plan your 10 maths lesson on: Checking and securing understanding of perimeter for compound shapes, download all teaching resources for free and adapt to suit your pupils' needs...