Idiot\'s Guides Basic Math and Pre-Algebra

Chapter 19: Graphs 267

MATH TRAP

Information given in percentages doesn’t automatically go in a circle graph. A circle

graph could show the percentages of the Town Council who come from each political

party, but it can’t show the percentage of Republicans in the Town Council compared to

the percentage of Republicans in the state legislature. The percentages have to be parts

of the same whole.

How to Draw It

Drawing a circle graph seems easy. Make a circle, add a few lines to split it up, and attach a few

labels. That will make a circle graph, but if you want a good circle graph, a really accurate circle

graph, it takes a bit more work.

Suppose County High School made a list of how many of its students came from each of the

towns in the county. Here’s what they found out.

Home Towns of County High Students

Town Number of Students

Arlington 274

Buxton 685

Carleton 137

Dover 411

Eatontown 548

To make an accurate circle graph, you first need to know what fraction of the high school enroll-

ment comes from each town. To find that out, total up all the students, and divide the number

from each town by the total of 2,055. Simplify the fractions.

Home Towns of County High Students

Town Number of Students Fraction of the School

Arlington (^2742055274) = 152
Buxton (^6852055685) =^13
Carleton (^1372055137) = 151
Dover (^4112055411) =^15
Eatontown (^5482055548) = 154