GRE Math : GRE Quantitative Reasoning

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #4 : Exponents And Rational Numbers

Solve for \(\displaystyle x.\)

\(\displaystyle 2^{x+1}=128\)

Possible Answers:

\(\displaystyle 8\)

\(\displaystyle 9\)

\(\displaystyle 7\)

\(\displaystyle 6\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 6\)

Explanation:

Recall that \(\displaystyle 128=2^7\)

With same base, we can write this equation: 

\(\displaystyle x+1=7\)

By subtracting \(\displaystyle 1\) on both sides, \(\displaystyle x=6\)

 

Example Question #32 : Algebra

Solve for \(\displaystyle x\).

\(\displaystyle 2^{x^2+4}=32\)

Possible Answers:

\(\displaystyle 5\)

\(\displaystyle -1, 1\)

\(\displaystyle -5\)

\(\displaystyle 1\)

\(\displaystyle -1\)

Correct answer:

\(\displaystyle -1, 1\)

Explanation:

Since \(\displaystyle 32=2^5\) we can rewrite the expression.

With same base, let's set up an equation of \(\displaystyle x^2+4=5\).

By subtracting \(\displaystyle 4\) on both sides, we get \(\displaystyle x^2=1\).

Take the square root of both sides we get BOTH \(\displaystyle 1\) and \(\displaystyle -1\)

Example Question #32 : Gre Quantitative Reasoning

Solve for \(\displaystyle x\).

\(\displaystyle 5^x=25^4\)

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 4\)

\(\displaystyle 10\)

\(\displaystyle 8\)

\(\displaystyle 5\)

Correct answer:

\(\displaystyle 8\)

Explanation:

They don't have the same base, however: \(\displaystyle 25=5^2\).

Then \(\displaystyle 25^4=(5^2)^4\). You would multiply the \(\displaystyle 2\) and the \(\displaystyle 4\) instead of adding.

\(\displaystyle 2\cdot 4=8\)

\(\displaystyle x=8\)

Example Question #33 : Gre Quantitative Reasoning

Solve for \(\displaystyle x\).

\(\displaystyle 4^{2x}=16^6\)

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 4\)

\(\displaystyle 8\)

\(\displaystyle 6\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 6\)

Explanation:

There are two ways to go about this.

Method \(\displaystyle 1:\)

They don't have the same bases however: \(\displaystyle 16=4^2\). Then \(\displaystyle 16^6=(4^2)^6\)

You would multiply the \(\displaystyle 2\) and the \(\displaystyle 6\) instead of adding. We have \(\displaystyle 2\cdot 6=2x\)

Divide \(\displaystyle 2\) on both sides to get \(\displaystyle x=6\).

 

Method \(\displaystyle 2\):

We can change the base from \(\displaystyle 4\) to \(\displaystyle 16.\)

\(\displaystyle 4^{2x}=(4^2)^x=16^x\) 

This is the basic property of the product of power exponents. 

We have the same base so basically \(\displaystyle x=6\)

Example Question #3 : Exponents And Rational Numbers

Solve for \(\displaystyle x\).

\(\displaystyle 1024^x=2\)

Possible Answers:

\(\displaystyle -\frac{1}{10}\)

\(\displaystyle -10\)

\(\displaystyle 2\)

\(\displaystyle \frac{1}{10}\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle \frac{1}{10}\)

Explanation:

Since we can write \(\displaystyle 1024^x=(2^{10})^x\)

With same base we can set up an equation of \(\displaystyle 10x=1\) 

Divide both sides by \(\displaystyle 10\) and we get \(\displaystyle x=\frac{1}{10}\)

Example Question #34 : Gre Quantitative Reasoning

Solve for \(\displaystyle x\).

\(\displaystyle 1024^x=\frac{1}{2}\)

Possible Answers:

\(\displaystyle \frac{1}{10}\)

\(\displaystyle -10\)

\(\displaystyle -\frac{1}{10}\)

\(\displaystyle 2\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle -\frac{1}{10}\)

Explanation:

\(\displaystyle 1024^x=(2^{10})^x\) 

We still don't have the same base however:  \(\displaystyle 2=\frac{1}{2}^{-1}\)

Then,

\(\displaystyle 1024^x=(2^{10})^x=\left[\left(\frac{1}{2}\right)^{-1}\right]^{10x}\).

With same base we can set up an equation of \(\displaystyle -10x=1\)

Divide both sides by \(\displaystyle -10\) and we get \(\displaystyle x=\frac{-1}{10}\)

Example Question #11 : Exponents And Rational Numbers

Quantitative Comparison: Compare Quantity A and Quantity B, using additional information centered above the two quantities if such information is given.

 

Quantity A             Quantity B

     43                              34 

Possible Answers:

The answer cannot be determined from the information given.

Quantity A is greater.

The two quantities are equal.

Quantity B is greater.

Correct answer:

Quantity B is greater.

Explanation:

In order to determine the relationship between the quantities, solve each quantity.

4is 4 * 4 * 4 = 64

34 is 3 * 3 * 3 * 3 = 81

Therefore, Quantity B is greater.

Example Question #32 : Algebra

Quantity A: \(\displaystyle (-1)^{137}\)

Quantity B: \(\displaystyle 0\)

Possible Answers:

The two quantities are equal.

Quantity A is greater.

The relationship cannot be determined from the information given. 

Quantity B is greater.

Correct answer:

Quantity B is greater.

Explanation:

(–1) 137= –1   

–1 < 0

(–1) odd # always equals –1.

(–1) even # always equals +1.

Example Question #1 : How To Find A Rational Number From An Exponent

\(\displaystyle 2^{-5}\)

 

Possible Answers:

\(\displaystyle -\frac{1}{32}\)

\(\displaystyle 2\)

\(\displaystyle 32\)

\(\displaystyle -32\)

\(\displaystyle \frac{1}{32}\)

Correct answer:

\(\displaystyle \frac{1}{32}\)

Explanation:

Anything raised to negative power means \(\displaystyle 1\) over the base raised to the postive exponent. 

\(\displaystyle 2^{-5}=\frac{1}{2^5}=\frac{1}{32}\)

Example Question #38 : Gre Quantitative Reasoning

Which of the following is not the same as the others?

Possible Answers:

\(\displaystyle (\frac{1}{2})^{^{-24}}\)

\(\displaystyle 64^4\)

\(\displaystyle 16^8\)

\(\displaystyle 2^{24}\)

\(\displaystyle 4^{12}\)

Correct answer:

\(\displaystyle 16^8\)

Explanation:

Let's all convert the bases to \(\displaystyle 2\).

\(\displaystyle 4^{12}=[2^2]^{12}=2^{24}\)

\(\displaystyle 64^4=(2^6)^4=2^{24}\)

\(\displaystyle 16^8=[2^4]^8=2^{32}\)

\(\displaystyle \left(\frac{1}{2}\right)^{^{-24}}\) This one may be intimidating but \(\displaystyle 2=\frac{1}{2}^{-1}\).

Therefore, 

\(\displaystyle \left(\left[\frac{1}{2}\right]^{-24}\right)^{-1}=2^{24}\)

\(\displaystyle 2^{24}\)

\(\displaystyle 16^8\) is not like the answers so this is the correct answer.

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