Proportions

This lesson will help you identify proportions when given two ratios.

Definition:

When two ratios are equal, we say that they form a proportion.

Look at the following two ratios:

3/5 and 6/7

Do they form a proportion?

You can tell if two ratios are equal by comparing their cross products. If the cross products are equal, then they form a proportion.

Recall that a cross product is obtained when you multiply the numerator of one fraction by the denominator of another fraction.

The cross products for 3/5 and 6/7 are

3 times 7 = 21 and

5 times 6 = 30

21 is not equal to 30. Therefore, 3/5 and 6/7 do not form a proportion.

Another example: Do 10/16 and 5/8 form a proportion?

10 times 8 = 80 and

16 times 5 = 80

80 is equal to 80, therefore, they form a proportion.

Notice also that 10/16 and 5/8 are equivalent fractions.

In general, if two fractions are equivalents, they form a proportion

Ratios

Ratios and proportions

Proportions

Solving proportions

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