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At a Glance - Pie Charts/Circle Graphs

Pie Charts
, also known as circle graphs, are ways of displaying the proportions, or percentages, of data that fall into different categories. It makes sense that these graphs are useful for displaying categorical data.

To make a pie chart, we start with a circle and cut it into slices like a pizza. Yeah, it would probably make more sense if we went with a "pie" analogy, but where's the fun in being predictable?

If half the data (50%) falls into one category, its corresponding slice will be half (50%) of the pizza. If one-eighth of the data falls into one category, its corresponding slice will be one-eighth of the pizza, and so on. Our advice is not to invite too much data to your house when you're throwing a party, so that you can keep most of the pizza for yourself.

Sample Problem

Thinking about backpacks helps us get to our happy place, so we'll do so once again. Suppose students had the following colors of backpacks:

red, blue, red, red, red, blue, green, green

There are 8 backpacks total. Half the backpacks are red, one quarter are blue, and one quarter are green. We can represent this by the following circle graph:

In this graph, we colored each individual slice of the graph with the backpack color it represented. We could instead have a key that explains what each color means. It may not be necessary in this example, but sometimes you'll have super-duper thin slices, so it's a good idea to get some practice. If, on the other hand, one of your special skills is the ability to replicate classic works of art on the head of a pin, you may have no need for a key.

If you're making pie charts and you don't have different-colored writing utensils handy, instead of making the pizza slices different colors you can just label each slice with the thing it represents. The important thing is to be able to tell the slices apart. If that means drawing a different Black Eyed Pea inside each one, so be it. Whatever works for you. Just make sure Fergie has the biggest slice. You know she'll get all "diva" about it.

Example 1

Use a pie chart to show the distribution of animals in a zoo that contains 40 penguins, 20 polar bears, 10 llamas, and 10 jaguars. Well, at least the penguins outnumber the jaguars, so they might have a fighting chance if all of them get loose. #yeahright

Example 2

The pie chart shows the favorite pie flavors of the students in Kelly's class. Use the pie chart to determine if each statement is true or false. Not that it's essential to this exercise, but note the measure of the ratio of the circumference of this chart to its diameter. Also pi. Freaky.

  1. One quarter of the students in Kelly's class like pumpkin pie best.
  2. More than half the students in Kelly's class like blueberry pie best.
  3. Less than one eighth of the students in Kelly's class like pecan pie best.
  4. An equal number of the students like cherry pie and lemon meringue best.
  5. Less than one eighth of the students like cherry pie best.

Exercise 1

Draw a pie chart (circle graph) for the following set of data:

Mrs. Leahy has 4 cats, 4 dogs, and 4 fish.

Exercise 2

Draw a pie chart (circle graph) for the following set of data:

Of the 60 kids in Jimmy's class, 30 ride the bus to school, 20 get rides from their parents, and 10 walk.

Exercise 3

Draw a pie chart (circle graph) for the following set of data:

A poll of Nancy's book club revealed that everyone liked chocolate. Four members preferred dark chocolate, and 6 members preferred milk chocolate. Maybe Nancy's book club should spend less time eating and more time reading. Just a thought.

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