Solving Proportions

GED Math

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.
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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.




Padlet

Click on the link to post questions or comments regarding what you have learned about proportions.


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