A **ratio** is a comparison of two quantities. For example, if a class consists of 15 women and 10 men, the ratio of women to men is 15 to 10. This ratio can also be written as 15:10 or \(\frac{15}{10}\)

Ratios, like fractions, can be reduced by dividing by common factors.

A **proportion** is a statement that two ratios are equal. For example, the proportion \(\frac{5}{10}=\frac{7}{14}\) is true because both ratios are equal to \(\frac{1}{2}\)

The **cross product** is found by multiplying the numerator of one fraction by the denominator of the other (*across* the equal sign).