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Circle Graphs to Display Data

Use percents to calculate the number of degrees needed for a circle graph.

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Circle Graphs to Display Data
License: CC BY-NC 3.0

Glenda is a reporter for the local television station and she is writing a story about the recent election for mayor. The percentages of the total votes received by each candidate are:

John Williams – 43%

Rachel Clark – 26%

Roger Parks – 19%

Paul Taylor – 12%

How can Glenda display these results on a graph that will allow viewers to quickly compare the results?

In this concept, you will learn to display data using circle graphs.

Circle Graphs

A circle graph, sometimes called a pie graph, is a visual way to display data using circles and parts of a circle. In fact, circle graphs are one of the most popular means of displaying real-world data.

License: CC BY-NC 3.0

In a circle graph, the entire circle represents 100% and each section of the circle represents some part out of 100.

The circle graph below shows how a graph is divided into sections according to the data. Data Set 1 is 25% of the graph. This is displayed numerically as well as visually. Notice that the green section of the circle is one-fourth, or 25%, of the circle.

License: CC BY-NC 3.0

Data Set 2 is 50% or one-half of the entire circle. Again, this is represented numerically and by the proportion of the circle it occupies.

Data Set 3, with 10%, and Data Set 4, with 15%, account for a total of one-fourth, or 25%, of the circle.

You can use circle graphs to easily answer questions about data and to compare and contrast sections of data with other sections and against the whole data set.

The circle graph below displays data about the spending habits of a teenager.

License: CC BY-NC 3.0

Even though this graph does not contain any numerical data, the way it is sectioned, you can estimate that 50% of this teen’s money went into savings, while 40% was spent on food and 10% of his money was spent on baseball cards.

Examples

Example 1

Earlier, you were given a problem about the election results from the mayor’s race.

Glenda has decided to display the results of the mayor’s race in a circle graph to accompany her story. She uses a program on her computer to design the circle graph. Now, she has to display the results on the graph. The results of the election are below.

John Williams – 43%

Rachel Clark – 26%

Roger Parks – 19%

Paul Taylor – 12%

How should the sections of the graph be proportioned and labeled so that viewers will be able to quickly compare the data?

First, take another look at Glenda’s data. The data is arranged and ordered.

John Williams – 43%

Rachel Clark – 26%

Roger Parks – 19%

Paul Taylor – 12%

Next, Glenda needs to create a circle graph with sections corresponding to the numerical data.

License: CC BY-NC 3.0

Then, she needs to add labels to help readers readily identify the data.

License: CC BY-NC 3.0

This is what Glenda’s finished circle graph should look like.

Example 2

Answer the following question about the data displayed in this circle graph.

License: CC BY-NC 3.0

What percent of the students aspire to work in science and research?

To figure this out, look at the whole of the circle and remember that it is equal to 100%.

First, note the known percentages.

20% want a career in healthcare.

15% want a career in the legal field.

10% want a career in law enforcement.

5% want a career in the military.

30% want a career in computers.

Then, there is an unknown percent of the students that want to work in science / research.

Next, add the known percentages and subtract the total from 100 percent.

20+15+10+5+3010080==8020

The answer is 20% of the students want a career in science and research.

Take a look at the circle graph below and answer the questions in the following examples.

License: CC BY-NC 3.0

Example 3

What is the most popular music selection?

First, look at the circle and choose the largest section.

Pop music covers half of the circle.

The answer is pop music.

Example 4

What percent of the students chose jazz music?

First, find the section on the graph corresponding to jazz music.

The yellow-shaded area represents jazz music.

The answer is one tenth, or 10 percent.

Example 5

What percent of the students chose country music?

To figure this out, look at the whole of the circle and remember that it is equal to 100%.

First, note the known percentages.

One quarter is the same as 25%, so 25% represents Rock music.

One tenth is the same as 10%, so 10% represents Jazz music.

One half is the same as 50%, so 50% represents pop music.

There is an unknown percent of the students that enjoy country music.

Next, add the known percentages and subtract the total from 100 percent.

25+10+5010085==8515

The answer is 15% of the students favor country music.

Review

Use the results of the survey, which is displayed in the circle graph, to answer each question.

A survey of 300 people asked them to name their favorite spectator sport. The results are shown in the circle graph below.

License: CC BY-NC 3.0

  1. What was the most favorite spectator sport of the people surveyed?
  2. What was the least favorite spectator sport of the people surveyed?
  3. What percent of the people surveyed said that football was their favorite spectator sport
  4. How many people said that basketball was their favorite spectator sport?
  5. How many more people said that soccer was their favorite sport than ice hockey?
  6. What percent of the people chose baseball and soccer as their favorite sports?
  7. What percent of the people did not choose baseball?
  8. What percent of the people did not choose hockey?
  9. What percent of the people chose tennis or soccer as their favorite sports?
  10. What percent of the people did not choose basketball or tennis?
  11. What percent of the people did choose tennis as a favorite sport?
  12. What percent of the people did not choose football?

The table shows the how much money the students in the seventh grade have raised so far for a class trip. Make a circle graph that shows the data.

Fundraiser Amount
Car Wash $150
Book sale $175
Bake sale $100
Plant sale $75
  1. Make a list of 5 popular ice cream flavors. Then survey your classmates asking them which of the 5 flavors is their favorite ice cream flavor. Use the data to make a circle graph.
  2. Use a newspaper to locate a circle graph of some data. Then write five questions about the data.
  3. Now create your own circle graph. Share it with a partner.

Review (Answers)

To see the Review answers, open this PDF file and look for section 10.11. 

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Vocabulary

\pi

\pi (Pi) is the ratio of the circumference of a circle to its diameter. It is an irrational number that is approximately equal to 3.14.

Area

Area is the space within the perimeter of a two-dimensional figure.

Diameter

Diameter is the measure of the distance across the center of a circle. The diameter is equal to twice the measure of the radius.

Pi

\pi (Pi) is the ratio of the circumference of a circle to its diameter. It is an irrational number that is approximately equal to 3.14.

Radius

The radius of a circle is the distance from the center of the circle to the edge of the circle.

Squaring

Squaring a number is multiplying the number by itself. The exponent 2 is used to show squaring.

Image Attributions

  1. [1]^ License: CC BY-NC 3.0
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