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Calculate the Third Angle in a Triangle

In this worksheet, students will calculate the third angle in a triangle.

'Calculate the Third Angle in a Triangle' 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

In this activity, we will learn how to identify the missing angle in a triangle. 


Remember: The angles in any triangle add up to a total of 180°


Let's try an example question together.



Here is a scalene triangle. 

All of its angles and sides are different.

What is the size of the angle marked with a question mark? 


Triangle 54-64-62



Here, we have been given two of the angles: 54° and 64°

To find the missing angle we need to add these two angles and subtract the total from 180.


54 + 64 = 118

180 - 118 = 62


The missing angle is 62°


We can check this is correct by doing: 54 + 64 + 62 = 180


green tick


Let's have a go at some questions now.

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