ACT Math : How to find percentage from a fraction

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Find Percentage From A Fraction

Luke went to the grocery store. It took him 15 minutes to drive to the store from his house, 30 minutes to shop, 5 minutes to put groceries in his car, and 20 minutes to drive home due to traffic.

What percentage of the trip did Luke spend inside his car?

Possible Answers:

45%

15%

50%

75%

35%

Correct answer:

50%

Explanation:

You take 15 + 20 = 35 minutes as total time spent in the car.

Then, you take 15 + 20 + 5 + 30 = 70 minutes as total trip time.

We take (35/70) x 100% = 50%

Example Question #1 : How To Find Percentage From A Fraction

There are 300 sandwiches at a company-wide picnic. If half of the sandwiches are tuna, and the provider mistakenly uses expired tuna in three-fifths of those sandwiches, what percentage of total sandwiches still remain edible?

Possible Answers:

\(\displaystyle 30\%\)

\(\displaystyle 40\%\)

\(\displaystyle 80\%\)

\(\displaystyle 70\%\)

 

\(\displaystyle 60\%\)

Correct answer:

\(\displaystyle 70\%\)

 

Explanation:

This multi-part question makes use of both fractions and percentages, as well as some tricky language if you are not paying close attention.

First off, determine what three-fifths of the 150 tuna sandwiches is:

\(\displaystyle 150 \cdot (\frac{3}{5}) = 90\)

Now, refer back to the question, which asks how many TOTAL sandwiches (tuna and non-tuna) still remain edible. This is simple arithmetic.

\(\displaystyle 300 - 90 = 210\)

Finally, find what percentage this equals:

\(\displaystyle \frac{210}{300} = 0.7=70\%\)

 

 

Example Question #2 : How To Find Percentage From A Fraction

Express the fraction \(\displaystyle \frac{7}{25}\) as a percentage.

Possible Answers:

\(\displaystyle 25\%\)

\(\displaystyle 30\%\)

\(\displaystyle 2.8\%\)

\(\displaystyle 28\%\)

\(\displaystyle 7\%\)

Correct answer:

\(\displaystyle 28\%\)

Explanation:

Converting a fraction to a percentage can be done in two ways.  The first way involves recalling that a percent is just a fraction of 100 (per cent).  Therefore, the percent equivalent to \(\displaystyle \frac{7}{25}\) is the numerator of the equivalent fraction whose denominator is 100.  In order to convert \(\displaystyle \frac{7}{25}\) to a fraction over 100, I need to multiply the numerator and denominator each by 4.

\(\displaystyle \frac{7}{25}\cdot \frac{4}{4}=\frac{28}{100}\)

Therefore, our answer is 28%.

 

The other approach is to convert the fraction to a decimal first by dividing 7 by 25.

\(\displaystyle 7\div25=0.28\)

To convert a decimal to a percent, just shift the decimal point two places to the right.

\(\displaystyle 0.28=28\%\)

With this method, our answer is again 28%.

Example Question #1 : How To Find Percentage From A Fraction

Convert to a percentage: \(\displaystyle \frac{3a}{2a^2}\)

Possible Answers:

\(\displaystyle a^{1.5} \%\)

\(\displaystyle 1.5^a \%\)

\(\displaystyle 300a^{2} \%\)

\(\displaystyle 150a^{-1} \%\)

\(\displaystyle \frac{3^a}{2^a} \%\)

Correct answer:

\(\displaystyle 150a^{-1} \%\)

Explanation:

Despite the presence of a variable, the rule remains the same: To convert a fraction to a percentage, multiply the numerator by 100 and solve the fraction.

\(\displaystyle \frac{3a}{2a^2} = (\frac{300a}{2a^2}) = 150a^{-1} \%\)

Example Question #11 : Percentage

A politician promises to spend a minimum of \(\displaystyle \frac{3}{8}\) of his budget on improving roads. What is the minimum percent of the budget that must be spent on roads to keep this promise?

Possible Answers:

\(\displaystyle 37.5 \%\)

\(\displaystyle 47 \%\)

\(\displaystyle 32.5 \%\)

\(\displaystyle 23.8 \%\)

\(\displaystyle 35.5 \%\)

Correct answer:

\(\displaystyle 37.5 \%\)

Explanation:

To find a percentage from a fraction, multiply the numerator by \(\displaystyle 100\), then solve the fraction.

\(\displaystyle \frac{3}{8} = (\frac{3 \cdot 100}{8}) \% = \frac{300}{8} \% = 37.5 \%\)

Thus, the politician must spend at least \(\displaystyle 37.5 \%\) of the budget on roads.

Example Question #3 : How To Find Percentage From A Fraction

Convert to a percentage: \(\displaystyle \frac{2}{5} + \frac{13}{15}\)

Round to the nearest integer.

Possible Answers:

\(\displaystyle 157 \%\)

\(\displaystyle 145 \%\)

\(\displaystyle 127 \%\)

\(\displaystyle 172 \%\)

\(\displaystyle 148 \%\)

Correct answer:

\(\displaystyle 127 \%\)

Explanation:

We can solve this problem either by adding the two fractions and then converting to a percentage, or by converting each fraction to a percentage before adding them. We'll use the first method in this case:

\(\displaystyle \frac{2}{5} + \frac{13}{15} = \frac{6}{15} + \frac{13}{15} = \frac{19}{15}\)

Now, just as before, multiply our numerator by \(\displaystyle 100\) and solve the fraction:

\(\displaystyle \frac{19}{15} = \left (\frac{1900}{15} \right ) \% \approx 127 \%\)

 

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