Unit 5 Section 4 : Angles on a Line and on a Point

Remember that

(a) angles on a line add up to 180


(b) angles at a point add up to 360

These are two important results which help when finding the size of unknown angles.

Example Questions

In the questions below, you need to use the facts above to work out the missing angles.
Practice Questions
Work out the answer to each of these questions then click on the button marked Click on this button below to see the correct answer to see whether you are correct.

(a) What is the size of angle A?

(b) What is the size of angle B?



Work out the answers to the questions below and fill in the boxes. Click on the Click this button to see if you are correct button to find out whether you have answered correctly. If you are right then will appear and you should move on to the next question. If appears then your answer is wrong. Click on to clear your original answer and have another go. If you can't work out the right answer then click on Click on this button to see the correct answer to see the answer.

Question 1
Calculate the unknown angle in each of the following diagrams.







Question 2
Calculate the unknown angle in each of the following diagrams.







Question 3
The diagram below shows a playground roundabout from above. Five metal bars are fixed to the centre of the roundabout as shown. The angles between the bars are all the same size.
(a) What size are the angles between the bars?

(b) What size would the angles be if there were 9 bars instead of 5?

Question 4
A boy hangs a punchbag on a washing line.
Both the unknown angles marked are the same size.
What is the size of each unknown angle?

Question 5
The diagram below shows two straight lines which cross each other.
Find the unknown angles.

a =

b =

c =

You should notice something about the angles which are opposite each other.

Question 6
In the diagram below, the large angle is 4 times bigger than the smaller angle.
Find the two unknown angles.

The smaller angle is
The larger angle is

Question 7
The diagram below shows a regular hexagon. The angles marked at the centre are all the same.
(a) What is the size of each angle marked at the centre of the hexagon?

(b) What would these angles be if the polygon was a decagon (10 sides)?

(c) If the centre angles were 30, how many sides would the polygon have?

You have now completed Unit 5 Section 4
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Produced by A.J. Reynolds January 2001