To solve for an unknown variable, first look at your remaining variables. The example problem will be 1/2 equals x/5. First, look at the denominators and divide them by each other. In this example, the answer for the denominators is 2.5. Now, look at the numerators and do the same to the bottom as you do to the top. For this example, you would multiply 2.5 times 1, which equals 2.5, your answer.