Cross-Multiplying Proportions

< Previous Lesson | Seventh Grade Lessons | Next Lesson >

Ratios: Learn

A proportion is an equation which states that two ratios are equal.

When the terms of a proportion are cross multiplied, the cross products are equal. To begin cross-multiplying, first write the ratios in fraction format.

Next, multiply the numerator of the first ratio by the denominator of the second, and also multiply the denominator of the first ratio by the numerator of the second.

21*10 = 70*3
210 = 210

The example above illustrates how the two ratios are actually equal. But cross-multiplying is most useful when one of the terms of the proportion is unknown. We usually represent unknown numbers with x.

Below is an example of finding an unknown term of a proportion using cross-multiplication.

10x = 70*3
10x = 210

10x

210

x = 21

Proportions: Practice

What is the missing term?

00:00

Determine the value of x by cross-multiplying.

then x =

Press the Start Button To Begin

You have 0 correct and 0 incorrect.

This is 0 percent correct.

Play

Game Name	Description	Best Score
	How many correct answers can you get in 60 seconds?	0
	Extra time is awarded for each correct answer. Play longer by getting more correct.	0
	How fast can you get 20 more correct answers than wrong answers?	999