Statistics: Basic Concepts

Pie Charts

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You’ve probably seen a **pie chart** before–they’re the charts that look like a pizza. Sometimes they’re also referred to as “pie graphs” or “circle graphs.”

Check out our video to learn more:

Characteristics of a pie chart

- This type of graph is good for comparing
**one type of variable**in a data set. - Each value in the data set is expressed as a
**percentage**and makes up a portion (or slice) of the graph. - When all of the slices are included, or 100% of the data, they form a
**360° circle**.

At a school, the girls’ basketball teams are having jackets made for the regional championship. The head coach wants to create a pie chart that shows which jacket sizes they’ll need.

**Step 1:**First, she organizes the data into a**table**. In Column 1, she records the sizes: extra small, small, medium, and large.- In Column 2, she writes down the
**frequency**, or the number of players who wear each size: 5 athletes wear an extra small, 10 prefer small, 26 for medium, and 19 for large. - Adding up these numbers gives us the
**total number of players**:**60**.

**Step 2:**She needs to figure out how many degrees each size will make up in the circle of the pie chart.- We know that a circle has
**360**°. If 360 is divided by the total number of players, 60, this tells us that**one athlete**=**6**°. - If we multiply 6 degrees by the number of players wearing each size, this tells us how big each section of the pie chart should be. For example,
**6****×****5 = 30**, so the extra small section should be**30****°**in the circle.

6 **×** 10 = **60****°** for size small,

6 **×** 26 = **156****°** for size medium,

and 6 **×** 19 = **114****°** for size large.

- To double-check her division, the coach adds up the numbers in Column 3. This equals
**360°**, which means that her calculations are correct.

**Step 3:**Finally, she adds Column 4, which will show the**percent of each size**.- If 100% represents the total and this is divided among 60 players, this means that
**one athlete = 1.7% of the team**(approximately). - So let’s multiply 1.7 by the number of players wearing each size to determine the percentages.

1.7 **×** 5 = **8.5% **for size extra small,

1.7 **×** 10 = **17%** for size small,

1.7 **×** 26 = **44.2%** for size medium,

and 1.7 **×** 19 = **32.3%** for size large.

Since 1.7% was an estimate, it’s okay if the sum of Column 4 goes a little over 100%.

**Step 4:**Now that the table’s complete, the coach begins making her**pie chart**. She traces her**protractor**to draw a circle.

**Step 5:**Then she measures a**30****°****angle**for size extra small. Next up is**60****°**for size small,**156****°**for size medium, and**114****°**for size large.

Then she adds the **percentage** to each slice of the pie, making the chart easier to read.

In the next lesson, we’ll show you how to make a **line graph**.

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