# Solving Proportions

## What is a proportion?

A proportion is a comparison between two equal ratios. Remember a ratio is a comparison between two related numbers. An example would be the ratio of boys to girls in a classroom or the amount of ginger ale and fruit juice in punch.

Often we use a ratio to figure out what we would like to know. For example, if we know there are 6 boys and 8 girls in a classroom we can use this to predict how many boys and girls there are in the entire school. Another example would be a punch recipe that calls for 2 liters of ginger ale for every gallon of fruit punch. How many liters of ginger ale are needed to make 5 gallons of fruit punch?

## Setting up a proportion

When setting up a proportion you must identify what you are comparing; that comparison is a ratio. Ratios always compare two different units/ingredients. Sometimes ratios can compare parts of a whole to the whole itself. In the example with the fruit punch we can set up a ratio comparing liters of ginger ale to gallons of fruit punch. We can write a proportion that helps us to solve the problem.

## Solving Proportions

There are several ways to solve proportions. Below are two of the more common methods. The third video demonstrates both methods and an additional example using algebra.