You can either multiply or divide both terms of the ratio by the same number to find equivalent rates. For example, if you run one mile in 10 minutes, you can use this rate to find out how many miles you could run in 40 minutes. To make the computations you need to begin with your word ratio to show the units of measure you’re comparing (mile/minutes). Now, you will fill in the terms, using the rate you know (1 mile/10 minutes). Next, you write another ratio, filling in the term you know and leaving the other blank (make sure you keep your units of measure in the same place) ___miles/40 minutes. If you wanted to write this as a proportion it would look like this:
1 mi = ___mi
10 min. 40 min.
Then, find out what was done to the like units. In other words, what was done to change the 10 min. into 40 min.? Since 10 x 4 = 40, we know that 4 was the factor used. Remember, whatever you do to the bottom ratio, you must do to the top. So, 1 must be multiplied by 4 to find the missing top term. This means the equivalent rate is 4 mi in 40 min.