4. Pie charts
Pie charts get their name because they look like a pie sliced up into pieces.
Learners like pie charts because they are often colourful and pleasing to the eye. However, accurately constructing pie charts requires substantial mathematical skills including proportional reasoning and using a protractor to measure angles, unless technology, such as a spreadsheet, is employed.
When introducing pie charts to learners it is common to start with circles split into 4, 8 or 16 slices. For example, here is a simple task for learners to try.
Classroom task
The school canteen needs to decide how many of each type of meal to produce so they note the meals selected by the next eight students in the canteen. The meal choices are meat, fish, vegetarian.
The choices that were recorded are below.
Some students will put the data in the diagram in the order given (figure 17A) whilst others may group the data first (figure 17B).
In deciding which presentation is better, the purpose of the data collection exercise should be considered – to inform the canteen what proportion of meals of each type to produce. Therefore, it is probably easier to see from Figure 17B that the canteen needs to produce the same amount of meat and vegetarian meals and slightly fewer meals containing fish (2 fish meals for every three meat/vegetarian meals).
It is possible to use this ‘equal slice’ method for creating pie charts to represent any number of items which is a factor of 360, although it does become significantly trickier to create the initial circle templates as the numbers get larger.