# Calculate Missing Sides in Similar Shapes

In this worksheet, students will calculate missing sides in similar shapes.

Key stage:  KS 3

Curriculum topic:   Geometry and Measures

Curriculum subtopic:   Interpret Mathematical Relationships Algebraically/Geometrically

Difficulty level:

#### Worksheet Overview

Remember, shapes that have the same size angles and are enlargements of each other are called  similar.

When we enlarge a shape we use a multiplier

We call it a scale factor

The shapes below are similar!

We can find the scale factor.

Large height ÷ Small height = 6 ÷ 2 = 3

or

Large base ÷ Small base = 3 ÷ 1 = 3

Both answers are 3, so the scale factor is 3

We can use this to find any missing sides. Let's try a question.

Example

The shapes below are similar.

Work out the length of the missing side, A.

To find the scale factor, we can divide the heights because we have both.

Scale factor = 12 ÷ 6 = 2

To find base A we can multiply the small base by the scale factor:

5 x 2 = 10

A = 10

Let's try some questions like this!

### What is EdPlace?

We're your National Curriculum aligned online education content provider helping each child succeed in English, maths and science from year 1 to GCSE. With an EdPlace account you’ll be able to track and measure progress, helping each child achieve their best. We build confidence and attainment by personalising each child’s learning at a level that suits them.

Get started