Easy Ways to Calculate Percentages

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How much is 15 percent of 210? How about 75 percent of 440 or 350 percent of 20? The standard way of calculating percentages can make these problems difficult to do without a calculator. Luckily, there are several tips and tricks you can use to solve percentage problems without a calculator. Once you understand these simple methods, these questions become easy to solve.

What Does 'Percent' Mean?

It is valuable to know the origin of the term ​percent​ if you want to truly understand how to calculate a percentage. The word ​percent​ comes from the phrase per cent. ​Cent​ is a root that means one hundred, so per cent literally means per one hundred. For example, if you know that 30 percent of the students in a school are boys, that means that there are 30 boys per one hundred students. Another way to say this is that 30 out of 100 students are boys.

Generally, the way to figure out any percentage is to multiply the number of items in question, or ​X​, by the ​decimal​ form of the percent. To figure out the decimal form of a percent, simply move the decimal two places to the left. For example, the decimal form of 10 percent is 0.1. Then, to calculate what 10 percent of is, say, 250 students, simply multiply the number of students by 0.1.

10 \text{ percent of } 250 \text{ students } = 0.1 × 250 \text{ students} = 25 \text{ students}

Some Easy Percentages to Remember

If you can commit the percentage list below to memory, you will be able to calculate a wide variety of percentages without a calculator.

50 percent​ means ​half​. To calculate 50 percent of a number, simply divide it by 2. For example, 50 percent of 26 is 26 divided by 2, or 13.

25 percent​ means ​one fourth​. To calculate 25 percent of a number, simply divide it by 4. For example, 25 percent of 12 is 12 divided by 4, or 3.

10 percent​ means ​one tenth​. To calculate 10 percent of a number, simply divide it by 10 or move the decimal point one place to the left. For example, 10 percent of 230 is 230 divided by 10, or 23.

5 percent​ is ​one half of 10 percent​. To calculate 5 percent of a number, simply divide 10 percent of the number by 2. For example, 5 percent of 230 is 23 divided by 2, or 11.5.