How to Do Percentages

Percent is a way to express a number as a portion of 100.

Percent means "per hundred" and is the amount out of 100. The symbol (%) is a simplistic way to write a fraction that has a denominator of 100. As an example, instead of stating the man was sick 24 days out of 100 days, you could state, "he was sick 24 percent of the time." When working with percentage problems, write down the numerical information---this can help with finding the solution.

Instructions

1. Divide the number (N) by 100 to obtain a decimal, and then move the decimal point two places to the right to obtain your percentage (P).

   For example, if you have 100 items, what percent is N, where N=24?
   N / 100 = P
   24 / 100 = .24 or 24%

2. Convert a fraction or decimal to a percent by multiplying by 100.

   For example, 1 girl (N) out of 5 (T) receives an equal share of the money from a bake sale. Divide the given amount (N) by the total amount (T) and multiply by 100 for the percent (P).
   N/T x 100 = P
   1/5 x 100 = 20 or 20%

3. Convert a percentage to a fraction by dividing by 100 and then simplifying.

   20% = 20/100 = 1/5

4. Convert a percentage to a decimal by moving the decimal two places to the left.

   20% = 20.0 = .20
   200% = 200.0 = 2.0

5. Convert to like measurements before calculating percent. When determining a percentage of differing measurements, you must first have all elements the same.

   For example, to determine the percent of 2 inches out of 12 feet, first convert the feet to inches.
   12 inches = 1 foot
   12 x 12 = 144 inches

   2 inches is what percent of 144?
   2 = Percent x 144
   2 ÷ 144 = .0138
   Move the decimal point two places to the right of multiply by 100 for a percentage of 1.38%.

Tips & Warnings

• A fast way to calculate percentage is remembering the term "of" means multiplication. 20% of 24 = .20 x 24 = 4.80.

• The term "is" means equals in mathematical terms. 20% of 24 is Solution. 20% x 24 = Solution.

• When finding a percent of a percent, convert the known percentage to a fraction. For example, 85% of 80 = X% would be (85/100) x 80 = 68%.

References

• West Texas A&M University: Beginning Algebra Tutorial on Percent

Resources

• "How to Solve Word Problems in Algebra;" Mildred and Tim Johnson; 2000