A circle graph, also known as a pie chart, shows the makeup of a group of data based on the percentage of the total that each subgroup represents. For example, a circle graph might show the revenue from the four lines of business a company has in place or the amount of sales resulting from each store. Each slice of the circle graph represents a percentage. To find the percentage represented by each slice, you need to know the angle measure of the slice.

Measure the angle of the sector of the circle graph with a protractor. Line the straight edge of the protractor up with one of the radii that form the sector and then find the angle measure from where the other radius intersects the curved edge of the protractor.

Divide the angle measure by 360 because to find the portion of the circle represented by the sector. For example, if the sector measures 162 degrees, divide 162 by 360 to get 0.45.

Multiply the portion by 100 to convert to a percentage. In this example, multiply 0.45 by 100 to find that a sector measuring 162 degrees equals 45 percent of the circle graph.

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