**To add a percentage to a given number involves multiplying the base number by a decimal that represents the percentage fraction.** Adding two percentages together involves the opposite, or converting the percentages to fractions.

To calculate the addition or subtraction of percentages, it is first necessary to understand the relationship between a percentage and its decimal representation.

**To Add a Percentage to a Given Number**

Multiply the base number by 1 plus the percentage as a decimal. For example, to add 25 percent to the number 4: 4 x (1 + 0.25) = 4 x 1.25 = 5.

**To Add Two Percentages Together**

Convert the percentages to fractions with a common denominator and perform the simple addition operation. Then the answer may be converted back to a percentage. For example, to add 20 percent to 30 percent: 20 / 100 + 30 / 100 = 50 / 100 or 50 percent.