A pie chart is a circle graph
divided into pieces, each displaying the size of some related piece of
information. Pie charts are used to display the sizes of parts that make up
some whole.
Example 1:
The pie chart below shows the
ingredients used to make a sausage and mushroom pizza. The fraction of each
ingredient by weight is shown in the pie chart below. We see that half of the
pizza's weight comes from the crust. The mushrooms make up the smallest amount
of the pizza by weight, since the slice corresponding to the mushrooms is
smallest. Note that the sum of the decimal sizes of each slice is equal to 1
(the "whole" pizza").
Example 2:
The pie chart below shows the
ingredients used to make a sausage and mushroom pizza weighing 1.6 kg. This is
the same chart as above, except that the labels no longer tell the fraction of
the pizza made up by that ingredient, but the actual weight in kg of the
ingredient used. The sum of the numbers shown now equals 1.6 kg, the weight of
the pizza. The size of each slice is still the same, and shows us the fraction
of the pizza made up from that ingredient. To get the fraction of the pizza
made up by any ingredient, divide the weight of the ingredient by the weight of
the pizza. What fraction of the pizza does the sausage make up? We divide 0.12
kg by 1.6 kg, to get 0.075. This is the same value as in the pie chart in the
previous example.
Example 3:
The pie chart below shows the
ingredients used to make a sausage and mushroom pizza. The fraction of each
ingredient by weight shown in the pie chart below is now given as a percent.
Again, we see that half of the pizza's weight, 50%, comes from the crust. Note
that the sum of the percent sizes of each slice is equal to 100%. Graphically,
the same information is given, but the data labels are different. Always be
aware of how any chart or graph is labeled.
Example 4:
The pie chart below shows the
fractions of dogs in a dog competition in seven different groups of dog breeds.
We can see from the chart that 4 times as many dogs competed in the sporting
group as in the herding group. We can also see that the two most popular groups
of dogs accounted for almost half of the dogs in the competition. Suppose 1000
dogs entered the competition in all. We could figure the number of dogs in any
group by multiplying the fraction of dogs in any group by 1000. In the toy
group, for example, there were 0.12 × 1000 = 120 dogs in
the competition.
