First of all, remember that you are solving for the number of students who did not have to go to summer school. If 4 students did have to go, out of 28, then 24 students did not have to go. 28 - 4 = 24 To express this as a ratio, simply treat 24 as the numerator and 28 as denominator: Divide both numerator and denominator by 4 to reduce the ratio or fraction to the lowest terms. TIP: When reducing a fraction to its lowest terms, choose the biggest common number that can be used to divide both numbers. In this case, it is 4 because 24 can be divided by 4, and 28 can be divided by 4. Also, remember that ratios can be expressed in three ways: * in words—6 to 7 * using a colon—6:7 * and as a fraction— These are all equivalent forms of this ratio. Sometimes it's easier to work with ratios when expressed as fractions.