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Straight Lines: What's the Unknown Angle?

In this worksheet, students calculate the unknown angle on a straight line.

'Straight Lines: What's the Unknown Angle?' worksheet

Key stage:  KS 2

Year:  Year 5 Maths worksheets

Curriculum topic:   Geometry: Properties of Shapes

Curriculum subtopic:   Identify Angles at a Point

Popular topics:   Angles worksheets, Geometry worksheets

Difficulty level:  

Worksheet Overview

This activity is about calculating the unknown angle on a straight line.

The angles at a point on a straight line add up to 180°.

180° is half a complete revolution.


Angles on a straight line 180

 Notice that 35° + 145° = 180°

e.g. Find the missing angle in degrees.


Find the missing angle on a straight line


The missing angle is 180° - 65° = 115°

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