Math percentage problems can often be confusing since they can have many variations. Whether you need to find the percentage of a number or what percentage a number is of another, each type of problem fortunately follows a set formula to make it simpler. The problem of finding what number that 20 percent of is 8 can be solved with the formula a = p * x, where a is the comparative number, or number after the percent has been applied, p is the percentage amount and x is the original number.

Divide 20 percent by 100 to obtain its decimal form. Dividing 20 percent by 100 equals 0.2.

Set up an equation as 0.2x = 8, which means 20 percent of x equals 8.

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Solve the equation by dividing each side by 0.2. Dividing 0.2 from each side results in x = 40. Eight is 20 percent of 40.