Pie charts are often colour-coded so that you can tell what each slice represents. Which colour belongs to which category is given in what is called a "key".
Pie charts are a way of displaying data. They get their name because they look a bit like pies from above, with different sized slices of pie being cut depending on the data you have.
I your exam, you'll need to know both how to read pie charts, and also how to construct your own.
First things first, we need to know how to read the data represented in a pie chart.
The chart below represents the results of a survey on a class of 24 students to find out their favourite colours.
Looking at the graph we can tell straight away, that half the class picked blue as their favourite colour. Yellow came in second with a quarter of the class choosing it, then red and green joint last with an eigth each.
So by using the fractions of the circle, we can see that 12 students favour blue, 6 favour yellow, 3 favour green and 3 favour red.
To fully understand what a pie chart is you will need to know how to construct one
Constructing a Pie chart:
In order to construct a pie chart, we first need to find out the fraction of the total that each slice represents.
- First work out the total frequency. This can be done by adding all the frequencies together.
- Find the fraction of the total frequency for each colour. = Frequency/Total Frequency
- Then find the angle. = (Frequency/Total frequency) x 360
This will give you the angles shown in the table below, and then you just have to draw the graph using those angles.
|Blue||5||(5÷40)x360 = 45|
|Red||10||(10÷40) x 360 = 90|
|Green||10||(10÷40) x 360 = 90|
|Purple||15||(15÷40) x 360 = 135|
To draw a pie chart, follow the steps listed below:
- Draw a circle using a compass
- From the centre draw a line vertically up. This will be the 0° line.
- Using a protractor and the 0° line use the angles you worked out to plot the pie char
Follow the links below to see how this topic has appeared in past exam papers