 # Land Your Score: Brush up on Ratios

- May 11, 07:44 AM Comments 

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.

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