Unit 5 Section 2 : Measuring Angles
A protractor can be used to measure or draw angles.
Note

The angle around a complete circle is 360º.
The angle around a point on a straight line is 180º.
A right angle is 90º.

Example Question 1
Measure the angle CAB in the diagram shown.

To measure this angle, you must first place a protractor over the angle, with the centre of the protractor over the point of the angle.
Click on the angle once to see a protractor appear.
Look how the line AB lines up with the number 0 on the protractor scale. You need to follow the scale round and read the number where the line AC crosses the scale. Make sure you always read the scale starting from zero.
You can hide the protractor again by clicking it once.

What is angle CAB in the picture?
Example Question 2
Measure the reflex angle in the diagram shown (a reflex angle is more than 180º).

The easiest way to measure this angle is to measure the smaller angle and subtract it from 360º (a full circle).
Click on the angle once to see a protractor appear over the small angle.
Reading around the scale from zero, we can work out the smaller angle. Since there are 360º in a full circle we can take this angle
away from 360 to work out the size of the reflex angle.
You can hide the protractor again by clicking it once.
What is the reflex angle in the picture?

In the questions below, it may be difficult to measure the angles on your screen with a
protractor. The questions are the same as those on pages 71 and 72 in the 7A practice book, so you could measure the angles
on the page and type their values on the screen.
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
For each of the following angles, first estimate the size of the angle and then measure the angle to see how good your estimate was. Type in each measured angle and check whether it is correct.
Question 2
Estimate and measure the size of each of these reflex angles
Question 3
Pupils in class 7G did a survey about their favourite football teams. The pie chart below represents their results.
You have now completed Unit 5 Section 2
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Produced by A.J.Reynolds January 2001