Calculating percentages is one of the most practical applications of math. A shirt on sale for 25 percent off, a stock with a 5 percent increase, or a chemistry formula with 10 percent of a given liquid; all these require the ability to calculate percentages. There are multiple methods for calculating a percent. Four different options are shown below. The ability to apply them to everyday life is an important skill.

## Using a Calculator

In order to use a calculator to calculate a percent, you'll need to first **convert the percent to a decimal**. To change an integer to a decimal, move the decimal point two spaces to the left. At that point, 20 percent would become **.20** and 45 percent would become **.45,** and so on. Once you have converted the percent to a decimal, you can use any basic calculator to multiply the decimal and the number.

For example, if a car dealer is advertising a 15 percent discount, how much can you save on a $24,000 car?

Use a calculator to multiply (24,000)(.15) to get 3600. The car dealer's sale would save you $3,600.

## Using Estimation

When you don't have a calculator handy, using estimation is a valuable option for finding a percentage. You can find **10 percent** of a number by moving the decimal point one space. This is usually a good starting point for estimation. If you can find 10 percent of a number, you can use that to estimate other percentages.

For example, you might not be able to calculate 15 percent of 250 without a calculator, but you can find 10 percent of 250 is 25 by moving the decimal point one space to the left. 20 percent would be twice that number, or 50.

From there, you can assume that 15 percent of 250 would be larger than 10 percent and smaller than 20 percent. An educated guess would be that 15 percent of 250 is about halfway between 25 and 50.

## Using Paper and Pencil

You can apply the traditional paper-and-pencil method of calculating, using a simple trick. Remember the pattern, **"is over of equals percent over 100"**, to help you solve tricky percentage word problems.

For example, what percent of 16 is 2? Try applying the pattern.

**Is / of = % / 100** Plug in what you know 2 / 16 = x / 100

**Then cross multiply and solve** 200 = 16x 12.5 = x So, 2 is 12.5 percent of 16.

**The pattern can be applied to whatever information you have.** 5 is 30 percent of what number?

Is/ of = % / 100 Plug in what you know 5 / x = 30 / 100 30x = 500 x = 16.7

## Divide and Move the Decimal

One final option to calculate a percentage is to use division. If you have two numbers to work with, divide and change the decimal to a percent by moving the decimal point. For example, what percent is 60 of 200? Try dividing.

60 / 200 = 0.3 Move the decimal point 2 spaces to the **right** 0.3 = 30 percent So 60 is 30 percent of 200.