Ratio

A ratio is a comparison of two numbers. A colon (:) usually separates the numbers in a ratio. If we want to write the ratio of 6 and 9, we write it as 6:9 or as a fraction 6/9, and we say the ratio is six to nine.

Proportion

A proportion is an equation with a ratio on one side and an equal ratio on the other side.

If one of the four numbers in a proportion is unknown, cross multiplication can be used to find the unknown number. This is called solving the proportion. Question marks or letters are frequently used in place of the unknown number.

Example:

Using cross multiplication we see that 2 x n = 1 x 4. So, 2n = 4. Divide both sides by 2.

If we use proportions to estimate how fast a Major League player could run from home to first on a Babe Ruth League Field, first we set the problem up as a proportion.

Solve for n: 4.2/90 = n/60 Where 4.2 is the average Major League running time from home to first for right handers and "n" stands for a proportional running time on a Major League player on a Babe Ruth field.

Using cross multiplication we see that 90 x n = 4.2 x 60. So, 90n = 252. Divide both sides by 90.

In this activity, you are going the other direction. You are estimating a Major-League time for each student. From students' running times over the 60-foot distance you will estimate what their times would be over 90 feet.