# KS3 Bitesize

Maths

Perimeter

The perimeter of a shape is the distance around its edge. Finding the perimeter just means adding up the lengths of all its sides.

## Introduction

This Revision Bite covers:

## Simple shapes

The perimeter of a shape is the length of its boundary.

Think of an ant starting from one corner of a small box, measuring 3 cm by 4cm. Imagine it walks all the way around the edge of the box. What distance will it have walked?

Perimeter = 4 + 3 + 4 + 3 = 14 cm

When calculating the perimeter, remember to include the length of every side.

## Compound shapes

Sometimes the shape is more complicated. In this case you need to calculate 'missing' lengths and be particularly careful to include all the sides.

Perimeter = 2 + 2 + 3 + 3 + 5 + 5 = 20 cm

Question

A plan of a play area is shown below:

a) Calculate the length of x and y
b) Calculate the perimeter of the play area.

a) The length of the play area is 20m, so x = 20 - 8 =12m.

The width of the play area is 15m, so y = 15 - 5 = 10m.

b) Perimeter = 8 + 5 + 12 + 10 + 20 + 15 = 70m.

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