To calculate percentages, convert the percentage to a decimal and multiply it by the number in the problem. For example, to find 40 percent of 50, change it to 0.40 times 50, which gives you the result of 20.

There are several methods for solving a percentage problem. For example, 100 percent of a number is the same number. So 100 percent of 50 is 50. When you double the percentage to 200, you can just double the number as well, which means that 200 percent of 50 is 100.

Do the same when reducing a number. To find 50 percent of 50, solve the problem by simply cutting the number in half. Therefore 50 percent of 50 is 25.

When you have an uncommon percentage, such as finding 4 percent of 200, you can rearrange the numbers to find the same result. This means that instead of finding 4 percent of 200, you can find 200 percent of four, which would be four times two, or eight. This method serves as a faster way to solve a seemingly complex percentage problem without having to do difficult multiplication.

For the inverse, or finding what percentage one number is of another, divide the first number by the second. If you've scored 20 out of 25 on a quiz and want to know your score as a percentage, divide 20 by 25. This calculation has a result of 0.80, or 80 percent. A score of 20 out of 25 is the same as 80 percent.