We encounter proportions frequently in everyday life. When we cook, we add proportional measurements of ingredients. If you are arranging flowers in a vase, you might want to add 2 stems of one type of bloom for every 3 stems of another.

On the GMAT proportions appear in word problems involving mixtures and probability, but they are most frequently seen in ratios.

## Understanding ratios on the GMAT

The ratios you encounter on Test Day may be part to part (boys to girls = 2:1), part to whole (boys to all children = 2:3), or even measure to measure (miles per hour, dollars per gallon). Here I will remind you of a few key tips to help you brush up on ratios for the Quantitative Reasoning section.

**Ratio values are reduced by common factors.**If the quantities of items in a ratio have a common factor, reduce the values to get the ratio. For example, if a GMAT question involved a restaurant offering 6 types of sandwiches and 3 kinds of soup each day, the sandwich-to-soup ratio would not be 6:3, because that can be reduced; the ratio would be 2:1.- If you solve a ratio problem and do not see your answer among the choices, be sure to
**reduce the values to their lowest form**. The GMAT will not list 6:3 among answer choices; that ratio would be 2:1 instead. - If you know a ratio between quantities, you only know their proportional relationship.
**You do not know actual values if you only know the ratio**. Think of ratios as having an invisible x; we write 3:2 (or 3/2), but the actual value is really 3x:2x (or 3x/2x). If you know a fruit basket contains oranges and apples in a ratio of 3:2, you might have 3 oranges and 2 apples. But you also could have 300 oranges and 200 apples; either way, the ratio remains 3:2.

- If you know a ratio between quantities, you know
**the actual value of each quantity will be a multiple of the ratio value**. For example, if the ratio of boys to girls in a certain classroom is 3:4, you know the number of boys is a multiple of 3 (because boys are represented by 3 in the ratio). The number of girls is a multiple of 4. And, because**you can add the parts gives to determine the ratio component of the total**, you know the number of children in the classroom is a multiple of 3+4, or 7. **If you know a:b and b:c, you can find a:c**. Imagine that the ratio of roses to carnations in a flower shop is 2:5, and the ratio of carnations to tulips is 7:3. You could write that as follows:

We can’t just “smush” these ratios together to say roses:tulips = 2:3; we need to **make the shared quantity the same**. Both ratios include a value for carnations, but they are different values. Find the least common multiple of the different values to make them the same. Multiply each ratio as needed to combine:

If we are asked to find the ratio of roses to tulips at this flower shop, we ignore the number of carnations and only look at roses and tulips; the ratio is 14:15.

Brushing up on ratios boosts your confidence as well as your score. Proportional relationships are constrained by a short list of tidy rules; spend some time learning them to land your best GMAT score on Test Day.

*Want to check your Quantitative Reasoning performance? Sign up for a **free GMAT practice test and review**.*

Jennifer Mathews Land has taught for Kaplan since 2009. She prepares students to take the GMAT, GRE, ACT, and SAT and was named Kaplan’s Alabama-Mississippi Teacher of the Year in 2010. Prior to joining Kaplan, she worked as a grad assistant in a university archives, a copy editor for medical web sites, and a dancing dinosaur at children's parties. Jennifer holds a PhD and a master’s in library and information studies (MLIS) from the University of Alabama, and an AB in English from Wellesley College. When she isn’t teaching, she enjoys watching Alabama football and herding cats.