GRE Math : Other Percentage

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #851 : Gre Quantitative Reasoning

\(\displaystyle s\) is \(\displaystyle r\) percent of \(\displaystyle 80\)

\(\displaystyle r\) is \(\displaystyle s\) percent of \(\displaystyle 125\)

Quantity A: \(\displaystyle s\)

Quantity B: \(\displaystyle r\)

Possible Answers:

Quantity B is greater.

The two quantities are equal.

Quantity A is greater.

The relationship cannot be determined.

Correct answer:

Quantity B is greater.

Explanation:

To attempt this problem, translate the statements into mathematical equations.  When you see the word 'is', it very often means 'equals:

\(\displaystyle s\) is \(\displaystyle r\) percent of \(\displaystyle 80\):

\(\displaystyle s=\frac{r}{100}80=\frac{4}{5}r\)

Now before we continue, look at this statement. We see that s is fourth fifths of r. That alone should tell us that r is greater!  However, we can continue with the calculations to see what these values are, if only for the sake of robustness. However, on the GRE, once you find the answer like this, fill it in and move on.

\(\displaystyle r\) is \(\displaystyle s\) percent of \(\displaystyle 125\)

\(\displaystyle r=\frac{s}{100}125=\frac{5}{4}s\)

Again, this validates our result. We may not know what r and s are, but we know how they relate to each other, and that is enough.

Quantity B is greater.

Example Question #261 : Arithmetic

\(\displaystyle 72\) is what percent of \(\displaystyle 120\) ?

Possible Answers:

\(\displaystyle 167\)

\(\displaystyle 117\)

\(\displaystyle 60\)

\(\displaystyle 17\)

\(\displaystyle 66\)

Correct answer:

\(\displaystyle 60\)

Explanation:

To solve this problem, translate \(\displaystyle 72\) is what percent of \(\displaystyle 120\) into mathematical terms:

\(\displaystyle 72=\frac{x}{100}120\)

\(\displaystyle x\frac{120}{100}=72\)

\(\displaystyle x=\frac{100}{120}(72)=\frac{100}{12*10}(12*6)=\frac{100}{10}(6)=10(6)=60\)

Example Question #11 : Other Percentage

In Dopolopolis, the first $20,000 dollars of a person's income is taxed at 6%, and any additional income they make is taxed at 10%. If Donny of Dopolopolis paid $2,000 in income tax this year, how much did Donny make?

Possible Answers:

\(\displaystyle 30000\)

\(\displaystyle 33333\)

\(\displaystyle 27000\)

\(\displaystyle 29000\)

\(\displaystyle 28000\)

Correct answer:

\(\displaystyle 28000\)

Explanation:

All of the answer choices are above $20,000, so assume that Donny paid the 6% on that:

\(\displaystyle 20000(0.06)=1200\)

That means of the $2,000 he paid in taxes

\(\displaystyle 2000-1200=800\)

$800 was taken from any income he made above the $20,000 line, and was thus taxed at 10%:

\(\displaystyle x(0.1)=800\)

\(\displaystyle x=8000\)

Donny's income must therefore have been

\(\displaystyle 20000+8000=28000\)

Example Question #12 : Other Percentage

Forty percent of the 20 professors in a university's physics department are male. If two male professors and two female professors retire, what percentage of the department will be male after the change?

Possible Answers:

\(\displaystyle 40\)

\(\displaystyle 37.5\)

\(\displaystyle 33.3\)

\(\displaystyle 60\)

\(\displaystyle 62.5\)

Correct answer:

\(\displaystyle 37.5\)

Explanation:

Begin by finding out how many of the 20 professors are male:

\(\displaystyle (20)(0.4)=8males\)

\(\displaystyle 20total-8males=12females\)

That means that there are eight males and twelve females currently to sum up to twenty.

Now, two males and two females leave, meaning the faculty is reduced by four:

\(\displaystyle 20-4=16\)

The amount of males has been reduced by two:

\(\displaystyle 8-2=6\)

Therefore, the percentage of the faculty that is male can be found as the number of males divided by the total faculty size times 100:

\(\displaystyle \frac{6}{16}100=37.5\)

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