# Graphs and Charts 3

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## Graphs and Charts 3

#### Pie charts

The whole key to pie charts is that they are made up of 3600 (although some pie chart scales are split into 100 so you can use percentages). They are a good thing to use when the data is separated into categories. For example, voting in a general election.

#### Making pie charts

To work out the angle needed for each section (a fraction of 360):

Then use a protractor to measure each section.

Always fully label all angles and sections in a pie chart as you go along.

To find out the frequency that each section represents measure the angle for the section then:

#### Scatter diagrams

In real life data rarely falls into strict patterns and produces straight lines on a graph but there may be trends when looking to see if two things are related. For example, number of cars on the road and number of accidents.

To see if two things are related we can use a Scatter Diagram.

Simply plot crosses on a graph for the two things you are looking at.

The following types of results can happen:

If the data follows a 'trend' or 'correlation' we can draw a line of best fit showing the general slope of the data (you can just use your judgement to do this - it does not have to actually pass through any of the points, it just needs to be roughly through the middle of them!). You can then get further information from the graph by using your line of best fit.

The graph below shows a class of pupils' Science exam results plotted against their Maths exam results. As you can see there is positive correlation:

A pupil who scored 65% in their Science exam was absent for their maths exam but we can use the line of best fit to predict what they would have scored in their Maths exam:

We predict that they would have scored 55%.