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

Remember that
(a) angles on a line add up to 180º
and
(b) angles at a point add up to 360º
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

to see whether you are correct.

(a) What is the size of angle A?

(b) What is the size of angle B?

Exercises

Work out the answers to the questions below and fill in the boxes. Click on the

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

to see the answer.

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

(a) º
(b) º
(c) º
(d) º
(e) º
(f) º

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

(a) º
(b) º
(c) º
(d) º
(e) º
(f) º

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

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?
º

Question 5
The diagram below shows two straight lines which cross each other.

Find the unknown angles.
a = º
b = º
c = º
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 º
The larger angle is º

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?
º
(b) What would these angles be if the polygon was a decagon (10 sides)?
º
(c) If the centre angles were 30º, how many sides would the polygon have?

You have now completed Unit 5 Section 4

Your overall score for this section is

Correct Answers
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Incorrect Answers
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There were questions with wrong answers.
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Produced by A.J. Reynolds January 2001

Remember that (a) angles on a line add up to 180º
and (b) angles at a point add up to 360º