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For example, 60% = 60 100 and we can simplify 60 100 = 3 5 . Since the equation 60 100 = 3 5 shows a percent equal to an equivalent ratio, we call it a percent proportion    . Using the vocabulary we used earlier:

amount base = percent 100
3 5 = 60 100

Percent proportion

The amount is to the base as the percent is to 100 .

amount base = percent 100

If we restate the problem in the words of a proportion, it may be easier to set up the proportion:

The amount is to the base as the percent is to one hundred.

We could also say:

The amount out of the base is the same as the percent out of one hundred.

First we will practice translating into a percent proportion. Later, we’ll solve the proportion.

Translate to a proportion. What number is 75% of 90 ?

Solution

If you look for the word "of", it may help you identify the base.

Identify the parts of the percent proportion. .
Restate as a proportion. .
Set up the proportion. Let n = number . n 90 = 75 100

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Translate to a proportion: What number is 60% of 105 ?

n 105 = 60 100

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Translate to a proportion: What number is 40% of 85 ?

n 85 = 40 100

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Translate to a proportion. 19 is 25% of what number?

Solution

Identify the parts of the percent proportion. .
Restate as a proportion. .
Set up the proportion. Let n = number . 19 n = 25 100
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Translate to a proportion: 36 is 25% of what number?

36 n = 25 100

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Translate to a proportion: 27 is 36% of what number?

27 n = 36 100

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Translate to a proportion. What percent of 27 is 9 ?

Solution

Identify the parts of the percent proportion. .
Restate as a proportion. .
Set up the proportion. Let p = percent . 9 27 = p 100
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Translate to a proportion: What percent of 52 is 39 ?

n 100 = 39 52

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Translate to a proportion: What percent of 92 is 23 ?

n 100 = 23 92

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Translate and solve percent proportions

Now that we have written percent equations as proportions, we are ready to solve the equations.

Translate and solve using proportions: What number is 45% of 80 ?

Solution

Identify the parts of the percent proportion. .
Restate as a proportion. .
Set up the proportion. Let n = number. .
Find the cross products and set them equal. .
Simplify. .
Divide both sides by 100. .
Simplify. .
Write a complete sentence that answers the question. 36 is 45% of 80.
Check if the answer is reasonable. Yes. 45 is a little less than half of 100 and 36 is a little less than half 80.
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Translate and solve using proportions: What number is 65% of 40 ?

26

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Translate and solve using proportions: What number is 85% of 40 ?

34

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In the next example, the percent is more than 100 , which is more than one whole. So the unknown number will be more than the base.

Translate and solve using proportions: 125% of 25 is what number?

Solution

Identify the parts of the percent proportion. .
Restate as a proportion. .
Set up the proportion. Let n = number. .
Find the cross products and set them equal. .
Simplify. .
Divide both sides by 100. .
Simplify. .
Write a complete sentence that answers the question. 125% of 25 is 31.25.
Check if the answer is reasonable. Yes. 125 is more than 100 and 31.25 is more than 25.
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Translate and solve using proportions: 125% of 64 is what number?

80

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Translate and solve using proportions: 175% of 84 is what number?

147

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Percents with decimals and money are also used in proportions.

Practice Key Terms 3

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Source:  OpenStax, Prealgebra. OpenStax CNX. Jul 15, 2016 Download for free at http://legacy.cnx.org/content/col11756/1.9
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