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Round circular graphs are known as pie charts. That name gave us an idea – what if they were made from pies?

Safety: When dealing with food, use clean hands and clean equipment!

You will need

• About 10 people
• 3 different circular pies, about the same size. Open topped tarts of different colours are best.
• Paper
• Pens
• Protractor
• Knife

What to do

What’s happening?

Pie charts are graphs. They are often used to show how something limited is shared. For example, a pie chart is good for showing how many hours a day you spend doing different things, or what you spend all your money on.

To make a pie chart, convert all the quantities you have into angles. You want two important things to happen. First, the proportions need to remain the same. If you spend twice as long reading as watching TV, you want the reading angle to be twice as large as the TV angle. Second, all the angles need to add up to 360°, or they won’t make a whole circle.

The angles at the centre of the circle show the relative sizes of the things you are graphing. Importantly, the areas of the pieces also show this information. If you change the length of the pieces, so some of them are segments of larger circles, the area behaves differently. If you make a pie piece twice as long, keeping the angle the same, it will have four times the area. Although it can look good to make some slices longer, it can make the graph misleading.