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A pie chart is a way of representing data, and comparing two or more different bits of data. For example, businesses represent their profits using pie charts, the segments of the pie chart showing where the profits are coming from.

From wikipedia:
A pie chart (or a circle graph) is a circular chart divided into sectors, illustrating proportion. In a pie chart, the arc length of each sector (and consequently its central angle and area), is proportional to the quantity it represents. When angles are measured with 1 turn as unit then a number of percent is identified with the same number of centiturns. Together, the sectors create a full disk. It is named for its resemblance to a pie which has been sliced. The earliest known pie chart is generally credited to William Playfair's Statistical Breviary of 1801.^{[1]}^{[2]}
The pie chart is perhaps the most widely used statistical chart in the business world and the mass media.^{[3]} However, it has been criticized,^{[4]} and some recommend avoiding it,^{[5]}^{[6]}^{[7]}^{[8]} pointing out in particular that it is difficult to compare different sections of a given pie chart, or to compare data across different pie charts. Pie charts can be an effective way of displaying information in some cases, in particular if the intent is to compare the size of a slice with the whole pie, rather than comparing the slices among them.^{[1]} Pie charts work particularly well when the slices represent 25 to 50% of the data,^{[9]} but in general, other plots such as the bar chart or the dot plot, or nongraphical methods such as tables, may be more adapted for representing certain information. It also shows the frequency within certain groups of information.

Pie Chart
Pie Chart  A special chart that uses "pie slices" to show relative sizes of data.Imagine you just did a survey of your friends to find which kind of movie they liked best.
Here are the results:
Table: Favorite Type of Movie Comedy Action Romance Drama SciFi 4 5 6 1 4 You could show that by this pie chart:

Pie charts are useful to compare different parts of a whole amount. This is used for statistical representation of data as a chart. For e.g. to represent precentage of items sold by a company in category wise.
Pie chart consists of a circle divided into several segments. Area of each segments is of the same percentage of the circle as the component it represents the whole data set.
Suggested reading…
Draw and interpret pie charts
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.
Example:
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.
Colour  Frequency  Angle 
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 
Total  40  360 
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
AQA Unit 1 March 2011 (F)  Page 9, Question 5c
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