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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

Curriculum topic:  Geometry: Properties of Shapes

Curriculum subtopic:  Identify Angles at a Point

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

This worksheet 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°

 

Example

Find the missing angle in degrees.

 

Find the missing angle on a straight line

 

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

 

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 20

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 140

Calculate the unknown angle in degrees.  (Just write the number)

 

 

Unknown angle 120

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 40

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 60

  • Question 1

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 20

CORRECT ANSWER
160
EDDIE SAYS
180 - 20 = 160
  • Question 2

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 140

CORRECT ANSWER
40
EDDIE SAYS
180 - 140 = 40
  • Question 3

Calculate the unknown angle in degrees.  (Just write the number)

 

 

Unknown angle 120

CORRECT ANSWER
60
EDDIE SAYS
180 - 120 = 60
  • Question 4

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 40

CORRECT ANSWER
140
EDDIE SAYS
180 - 40 = 140
  • Question 5

Calculate the unknown angle in degrees.  (Just write the number)

 

Unknown angle 60

CORRECT ANSWER
120
EDDIE SAYS
180 - 60 = 120
---- OR ----

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