How Do I Calculate the Percentage of a Sum?
To find the percentage of a number, multiply the number by the percentage fraction. A percentage is a proportion between two quantities expressed in hundredths.

Calculate the percentage fraction
Value of a percentage is the same as the numerator in a percentage fraction. The numerator of a fraction is the number on top. For example, 15 percent is the same as 15/100, which can also be written as 0.15. A simple way to find the percentage fraction is to move the decimal of the percentage two places to the right.

Multiple the sum by the percentage fraction
Multiply the sum by the percentage fraction to find the percentage of the sum. For example, if you want to find the 15 percent of the total sum 3500. To find 15 percent of 3500, multiply 3500 by 0.15. 3500 x 0.15 = 525

Explain the answer
Once you have the result of your calculations, explain the answer in context. For example, 15 percent of 3500 equals 525. Calculating percentage is useful for several areas of life, including restaurant tipping, commissions, sales tax and income tax. For example, to calculate a 20 percent tip on a $45 restaurant bill, multiply $45 by 0.2 to get the result, which is a $9 tip.