Reading Circle GraphsReading Circle Graphs

Section 8.2

Circle GraphsCircle Graphs

A A circle graphcircle graph is often used to show is often used to show percents in different categories, with percents in different categories, with the whole circle representing 100%.the whole circle representing 100%.

2Martin-Gay, Prealgebra, 5ed

A telephone survey was taken to identify favorite sport A telephone survey was taken to identify favorite sport activities. The results of the four most popular activities activities. The results of the four most popular activities are shown in the form of a circle graph below.are shown in the form of a circle graph below.

Walking 37%

Swimming 25%

Biking 21%

Bowling 17%

3Martin-Gay, Prealgebra, 5ed

Drawing Circle GraphsDrawing Circle Graphs

To draw a circle graph, we use the fact To draw a circle graph, we use the fact that a whole circle contains 360that a whole circle contains 360° ° (degrees).(degrees).

360°

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The following table shows the percent of U.S. The following table shows the percent of U.S. armed forces personnel that are in each branch of armed forces personnel that are in each branch of the service. the service.

Branch of ServiceBranch of Service PercentPercent

ArmyArmy 33%33%

NavyNavy 27%27%

Marine CorpsMarine Corps 12%12%

Air ForceAir Force 25%25%

Coast GuardCoast Guard 3%3%

Source: U.S. Department of Defense5

To draw a circle graph showing this data, we find To draw a circle graph showing this data, we find the number of degrees in each sector representing the number of degrees in each sector representing each branch of service.each branch of service.

SectorSector Degrees in Each SectorDegrees in Each Sector

ArmyArmy 33% x 360° 119 °

NavyNavy 27% x 360° 97°

Marine CorpsMarine Corps 12% x 360° 43 °

Air ForceAir Force 25% x 360° 90 °

Coast GuardCoast Guard 3% x 360° 11°

6Martin-Gay, Prealgebra, 5ed

We draw a circle and mark its center. Then We draw a circle and mark its center. Then we draw a line from the center of the circle to we draw a line from the center of the circle to the circle itself.the circle itself.

We use a protractor to construct the sectors. We use a protractor to construct the sectors. We place the hole in the protractor over the We place the hole in the protractor over the center of the circle. Then we adjust the center of the circle. Then we adjust the protractor so that 0protractor so that 0° on the protractor is ° on the protractor is aligned with the line that we drew.aligned with the line that we drew.

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To construct the “Army” sector, we find 119To construct the “Army” sector, we find 119° on ° on the protractor and mark our circle. Then we the protractor and mark our circle. Then we remove the protractor and use this mark to draw a remove the protractor and use this mark to draw a second line from the center to the circle itself.second line from the center to the circle itself.

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To construct the “Navy”sector next, we follow the To construct the “Navy”sector next, we follow the same procedure as before except that we line 0same procedure as before except that we line 0° up ° up with the second line we drew and mark the with the second line we drew and mark the protractor this time at 97°.protractor this time at 97°.

9Martin-Gay, Prealgebra, 5ed

We continue in this manner until the circle We continue in this manner until the circle graph is complete.graph is complete.

10Martin-Gay, Prealgebra, 5ed