Proportions

A proportion is simply a statement that two ratios are equal A proportion is simply a statement that two ratios are equal. It can be written in two ways: as two equal fractions a/b = c/d; or using a colon, a:b = c:d.

We can also cross multiply to find a missing term in a proportion We can also cross multiply to find a missing term in a proportion. Here's an example:

In a horror movie featuring a giant beetle, the beetle appeared to be 50 feet long. However, a model was used for the beetle that was really only 20 inches long. A 30-inch tall model building was also used in the movie. How tall did the building seem in the movie?

First, write the proportion, using a letter or symbol to stand for the missing term. 50 = ? 20 30

Next, simply cross multiply the two numbers we know. 50 = ? 20 30 50 x 30= 1,500

Next, we divide by the number we didn’t use to find out our missing number. 50 = ? 20 30 20)1500

Finally, we solve! 75 20) 1500 - 1 4 0 1 0 0 - 10 0

Example: 25 = 4 t 10 Find t:

Example: 210 = ? 8 2 Find ?: