How to Calculate Proportions

Proportions can be seen in many aspects of living. From mixing baby formula to describing how to divide a pie amongst children, proportions are very useful to describe the relationship between two quantities.

Things You'll Need

• Writing utensil
• Something to write on

Instructions

Computing proportions

1. Define the problem. In order to compute a proportion, the two quantities being compared must be known. For simplicity, let them be called A and B.

2. Determine which quantity is being divided. The quantity being divided usually appears before a "to" or "per" in a problem, and it is being divided by the number after. For example, in miles per gallon, the total number of miles is being divided by the number of gallons used.

3. Express the quantities as numbers. In order to compute the proportion, numbers are used and divided to obtain the result.

4. Perform the division. Suppose there are 50 of A and 10 of B. Then the proportion is:A/B = 50/10 = 5 A per B.

5. Use the proportion as needed. For example, suppose that I have 30 B now. Then according to the proportion of 5 A per B, I have:30 B times 5 A per B is 30*5 = 150 A.

Tips & Warnings

• When you have three or more quantities, you can compute more than one ratio. For example, I can have A per B and B per C. Combining these two gives A per C.