Why do you use circle graphs for percents?

Answer 1

Because it's a nice visual tool, and all the segments will add to a complete whole.

To fill in a pie chart with percents (that all add up to 100%), here's what you do:

(1) Identify the percent of the circle that you want to fill in. Say you want to color 45% of the circle red--that's a pretty big slice. Keep in mind that 45% in decimal form is 0.45 (I just moved the decimal over two places to the left).

(2) Take that decimal, 0.45 in this case, and multipy it by 360, because there are 360 degrees in a complete circle. 0.45*360 = 162, so you will color 162 degrees of the 360 degree circle.

(3) Use a protractor to draw a circle (one half at a time, probably) complete with an origin, the point in the very middle. Also draw one straight line (anywhere) from the origin to the edge of the circle.

(4) Place the 0 degree line on your protractor over the line you just drew. Using the marks on your protractor, mark on the edge of your circle where 162 degrees is, in reference to the first straight line.

(5) Remove your protractor and draw another straight line from the 162 degree mark you made on the edge of your circle to the origin. Between those two lines is 162 degrees, or 45% of a complete circle.

This is process can be repeated for any percentage between 0 and 100.