An equation that tells us that one ratio is equal to another ratio is called a

proportion.

A baseball team wins 15 games out of 30 games played. If the team continues

to win at the same rate, how many games will it win out of 40 games played?

a. Let N = number of games the team will win in 40 games played.

b. The ratio of games won to games already played is 15/30. Since the ratio of

games won to games played is to remain the same, we may write this ratio as N/40.

These ratios may also be written as 15:30 and N:40.

c.

We may now write the equation 15/30 = N/40. This is our proportion.

1 2

Proportions have a very useful property. Consider the proportion: 3 = 6 or 1:3 =2:6.

a. The two inside terms (3 and 2) are called the "means" of the proportion, and

the two outside terms (1 and 6) are called the "extremes" of the proportion.

b. Notice that if we multiply the two means, we obtain 3 x 2 = 6. Also, if we

multiply the two extremes, we obtain 1 x 6 = 6. This illustrates the following property of

proportions:

**In a proportion, the product of the means is equal to the product of the extremes.**

3:4. If a tank contains 24 quarts of alcohol, how many quarts of

water must be added to make the antifreeze mixture?

Let X = the number of quarts needed.

alcohol

3 = 24

water

4

X

MD0904

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