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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.

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