Percents are helpful in solving many practical problems. Here is a selection of some of their most common uses. Finding percents of a number. To find a certain percentage of some given number, change the percent to a decimal or fraction (whichever you prefer) and multiply. In these problems, it can help to think of the word "of" as meaning multiply. Finding what percent one number is of another number. One way to find what percent one number is of another number is the division method. To use this method, take the number after the word of and divide it into the number next to the word is. Then change the answer to a percent. Finding a number when a percent of it is known. The division method can also be used to find a number when a percent of it is known. To apply this method, take the percent, change it to a decimal or fraction, and divide that number into the other number. Finding percent increase or percent decrease. Often, we want to know by what percent something increased or decreases. There's a simple formula for finding percent change, whether it's increase or decrease. To find percent change, use the following formula: percent change = change / starting value