You can use a circle graph--sometimes called a pie chart--to illustrate the percentages represented by different groups within a larger population. For instance, a circle graph could be used to show the percentages of a high school's student population that are freshmen, sophomores, juniors, and seniors. A protractor is the perfect tool to use to make a circle graph because it allows you to section off exact portions of a circle by degrees. Using a protractor to make a circle graph is simple to do, given that you know the percentages you are working with.
Things You'll Need
Place your protractor on top of your piece of paper and use it to draw a complete circle. Do so by tracing 180 degrees along the outside edge of the curved portion of the protractor, then flipping the instrument upside-down and tracing the curve again.
Draw a dot in the exact center of your circle, which will be the midpoint of the outside edge of the straight portion of the protractor.
Write down the percentages you are working with. For instance, imagine that you are making a circle graph to represent a student body that is 28 percent freshmen, 27 percent sophomores, 25 percent juniors, and 20 percent seniors.
Calculate the number of degrees that should represent each group in your circle graph by multiplying each percentage, in decimal form, by 360--the total number of degrees in the circle. In our student body example:
Freshmen = 0.28 x 360 = 101 degrees
Sophomores = 0.27 x 360 = 97 degrees
Juniors = 0.25 x 360 = 90 degrees
Seniors = 0.20 x 360 = 72 degrees
The entire circle--360 degrees--represents the whole student body, and it can be divided into sections of 101, 97, 90, and 72 degrees, to represent the subgroups within the student body.
Line up the center dot of your circle with the midpoint of the straight edge of the protractor. Make a mark at 0 degrees on the curved edge of the protractor, which should be lined up with the edge of the circle. Then trace the circle in a clockwise direction until you reach the correct measurement for the first percentage in your graph. In our example, we would stop at 101 degrees and make another mark there.
Use the straight edge of your protractor to draw lines connecting the center of the circle to the first two marks you made on the outer edge of the circle. This "pie slice" represents the first part of the graph. In the case of our example, it represents the 28 percent of the student body that are freshmen.
Align the center of the protractor with the center of the circle, and rotate the instrument until the straight edge matches the line you drew to the second mark you made on the circle (the 101 degree mark in our example). This now becomes 0 degrees. Trace the outer edge of the protractor clockwise until you measure out the second portion of your graph. In our example, we would make the next mark at the 97 degree point. Once again, draw a line from the center to the new mark and label this next "pie slice" accordingly. In our example, the second "slice" represents the 27 percent that are sophomores.
Repeat the process of creating measured "pie slices" until you have completed the entire graph and represented all the groups.
- Photo Credit protractor image by timur1970 from Fotolia.com
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