Percent mean out of 100. A fractional percent is a percent that includes a portion of a percent, like 1/2%, 0.42%, 7 3/4%, or 4.5%. Percents can be written as fractions and as decimals. You can use mental math strategies such as halving, doubling, and dividing by ten to find the percents of some numbers. To calculate the percent of a number, write the percent as a decimal and then multiply by the number. Percents can be combined by adding to solve problems, like 5%+7%=12%.