Reading Circle Graphs Section 8.2

Circle Graphs A circle graph is often used to show percents in different categories, with the whole circle representing 100%. 2 Martin-Gay, Prealgebra, 5ed

A telephone survey was taken to identify favorite sport activities. The results of the four most popular activities are shown in the form of a circle graph below. Walking 37% Swimming 25% Biking 21% Bowling 17% 3 Martin-Gay, Prealgebra, 5ed

Drawing Circle Graphs To draw a circle graph, we use the fact that a whole circle contains 360° (degrees). 360° 4 Martin-Gay, Prealgebra, 5ed

The following table shows the percent of U.S. armed forces personnel that are in each branch of the service. Branch of Service Percent Army33% Navy27% Marine Corps 12% Air Force 25% Coast Guard 3% Source: U.S. Department of Defense 5

To draw a circle graph showing this data, we find the number of degrees in each sector representing each branch of service. Sector Degrees in Each Sector Army 33% x 360°  119 ° Navy 27% x 360°  97° Marine Corps 12% x 360°  43 ° Air Force 25% x 360°  90 ° Coast Guard 3% x 360°  11° 6 Martin-Gay, Prealgebra, 5ed

We draw a circle and mark its center. Then we draw a line from the center of the circle to the circle itself. We use a protractor to construct the sectors. We place the hole in the protractor over the center of the circle. Then we adjust the protractor so that 0° on the protractor is aligned with the line that we drew. 7 Martin-Gay, Prealgebra, 5ed

To construct the “Army” sector, we find 119° on the protractor and mark our circle. Then we remove the protractor and use this mark to draw a second line from the center to the circle itself. 8 Martin-Gay, Prealgebra, 5ed

To construct the “Navy”sector next, we follow the same procedure as before except that we line 0° up with the second line we drew and mark the protractor this time at 97°. 9 Martin-Gay, Prealgebra, 5ed

We continue in this manner until the circle graph is complete. 10 Martin-Gay, Prealgebra, 5ed