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All about Pie Charts
A pie chart is used to represent data that can be separated into segments. This means we can quite easily convert the data into things like percentages and decimals for each part. A circle is used for the chart and the circle segment represents the percentage of each particular piece of data.
To find the percentage that is represented by a segment of the pie chart we must measure its size using a protractor and then divide this amount by the total of 
. For example, if a segment takes up 
then this means that the percentage of the total will be 
%.
Example
The table below shows the number of pupils in a school and what year they are in.
| Year | Number of pupils |
|---|---|
| 1 | 20 |
| 2 | 30 |
| 3 | 10 |
| 4 | 40 |
Use a pie chart to represent this data and state the percentages of pupils in each year against the total number.
This question tells us the number of students in each year, so to get the total we must add these up to give 100. Now we can work out the size of a segment that represents one student and then use this to find the segments for each different amount in the table. Since we have 100 pupils that must make up all in the circle, each individual student must be shown as a segment the size of 
. Now we can work out the amount of the circle that each part must take up. So, for example, there are 20 students in year 1 meaning that the segment must be 
. Finding out each different segment size and then putting these together into the pie chart we get the graph shown below.
When working with pie charts we must ensure that we can make sense of the key that is shown to the right-hand side of the diagram. Looking at the colours of the different segments and the key to the side shows us which segment represents which part of the data.
Working backwards from a completed pie chart
Another method which we must perfect is to work from a pie chart that is given and to use this to work out the amounts represented by each section. To do this we simply reverse the steps used when drawing a pie chart:
1) First we must find the segment size for each part in the diagram.
2) Convert this segment size into a percentage or fraction of the entire circle.
3) Multiply this percentage by the total number of individual pieces of data in the situation (in the previous example this was 100 pupils) to get the amount for each section.
Example
The pie chart shows the different male and female workers in an office. If the total number of workers is 120, work out the number of workers that are female.
The segment size for females is 
, which when converted to a percentage with the full for a circle gives us 
. This is then multiplied by the entire number of workers which is 120 to give the actual number of female workers in the office as 45.
