In this lesson, we review how to work with ratios and rates. A ratio is a comparison of two quantities. It tells us how much of one thing there is compared to how much of another thing there is. A rate is a special type of ratio in which the units are different. Normally, we work with unit rates to find the amount of one thing per one unit of another. Lastly, we will look at proportions. A proportion tells us that two ratios or two rates are equal in value. We can check for proportionality via the equality test for fractions. For this test, we can say that two fractions are equal if and only if their cross products are equal.