By Mark Zegarelli

When you boil them down, nearly all percent problems are like one of the three types shown in the following table. In each case, the problem gives you two of the three pieces of information, and your job is to figure out the remaining piece.

The Three Main Types of Percent Problems
Problem Type What to Find Example
Type #1 The ending number 50% of 2 is what?
Type #2 The percentage What percent of 2 is 1?
Type #3 The starting number 50% of what is 1?

You probably are used to solving problems that look like this:

50% of 2 is ?

The answer, of course, is 1. Given two pieces of information — the percent and the number to start with — you can figure out what number you end up with.

Now suppose instead that the percent is left out but you are given the starting and ending numbers:

? % of 2 is 1

You can still fill in the blank without too much trouble. Similarly, suppose that the starting number is left out but you are given the percent and the ending number:

50% of ? is 1

Again, you can fill in the blank.