Percentages convert a ratio to being out of 100. For example, the ratio on-out-of-four is equivalent to 25 out of 100, so one out of four equals 25 percent. Percentages are useful for comparing ratios. You can also figure out the number out of a total that would be equal to a certain percentage. For example, you might want to know how many questions you need to get right on a test to get a certain percentage score.

Determine the percentage of the total you want to calculate. For example, a problem might ask you to find 28 percent of 66.

Divide the percentage that you want to find by 100 to convert it to a decimal. For example, if you want to find 28 percent, you would divide 28 percent by 100 to get 0.28.

Multiply the percentage expressed as a decimal by the total to find the amount that corresponds to the total. For example, if your total was 66, you would multiply 0.28 by 66 to get 18.48.