## Subjects

# Draw circle graphs

Which tool can be used to measure angles in a circle graph?

## Draw circle graphs

Here is a table that shows which ice cream flavours Leon’s friends like best. Four of them like strawberry, six like vanilla and eight like pear. To make it easier to compare how popular the three ice cream flavours are, we will make a graph from the table. By making a circle and dividing it into different parts, we can show what proportion of friends like the different flavours. To draw a circle graph, we need a pen, ruler, compass and protractor.

Mark the centre of the circle, the centre point. Put the needle of the compass in the centre point and draw a circle. The whole circle corresponds to all of Leon’s friends. How many friends are there? Four, plus six, plus eight… 18 friends.

A whole circle is 360 degrees, so 360 degrees corresponds to 18 friends. We want to show what proportion of friends like strawberry, vanilla or pear. If 18 friends corresponds to 360 degrees, then one friend must correspond to 360 divided by 18. That’s 20. One friend corresponds to 20 degrees on the circle.

And since four friends like strawberry, that part of the circle must be: 4 times 20 degrees - which is 80 degrees. We need to draw a wedge of 80 degrees in the circle. Draw a straight line from the centre point to the edge of the circle. Place the protractor on the centre point with the straight part facing the line you just drew. Mark 80 degrees with a small point.

Use the ruler to draw a line from the centre point to the small point. Colour this part red. This wedge is as big a part of the circle as the proportion of Leon’s friends who like strawberry ice cream best. Now we do the same with vanilla. Six out of the 18 friends like vanilla.

Six times 20 degrees is 120 degrees. Mark 120 degrees using the protractor. Draw a point. Draw a line. This part can be yellow.

The remaining part of the circle corresponds to the remainder of the friends — the eight of them who like pear best. Colour the pear part green. Now the circle graph is ready. Look at the graph. The surface of each part of the circle shows the proportion of friends who like a certain ice cream flavour.

Now we can easily compare how popular the different ice cream flavours are among Leon’s friends. It looks like Leon is going to have a party... and now he knows exactly what ice cream cake will make everyone happy!