GRE Math : How to find a rational number from an exponent

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #31 : Algebra

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 two quantities are equal.

Quantity A is greater.

Quantity B is greater.

The answer cannot be determined from the information given.

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

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

Quantity B: \displaystyle 0

Possible Answers:

Quantity B is greater.

Quantity A is greater.

The relationship cannot be determined from the information given. 

The two quantities are equal.

Correct answer:

Quantity B is greater.

Explanation:

(–1) 137= –1   

–1 < 0

(–1) odd # always equals –1.

(–1) even # always equals +1.

Example Question #13 : Exponents And Rational Numbers

\displaystyle 2^{-5}

 

Possible Answers:

\displaystyle -\frac{1}{32}

\displaystyle \frac{1}{32}

\displaystyle 32

\displaystyle 2

\displaystyle -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 #35 : Gre Quantitative Reasoning

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

Possible Answers:

\displaystyle 4^{12}

\displaystyle 64^4

\displaystyle 2^{24}

\displaystyle 16^8

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

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.

Example Question #41 : Algebra

Simplify

\displaystyle 2^{10}+2^9

Possible Answers:

\displaystyle 2^{10}

\displaystyle 2^9\cdot 3

\displaystyle 2^{19}

\displaystyle 2^{10}\cdot 3

\displaystyle 2^{18}\cdot 3

Correct answer:

\displaystyle 2^9\cdot 3

Explanation:

Whenever you see lots of multiplication (e.g. exponents, which are notation for repetitive multiplication) separated by addition or subtraction, a common way to transform the expression is to factor out common terms on either side of the + or - sign. That allows you to create more multiplication, which is helpful in reducing fractions or in reducing the addition/subtraction to numbers you can quickly calculate by hand as you'll see here.

 

So let's factor a \displaystyle 2^9.

We have \displaystyle 2^9(2+1).

And you'll see that the addition inside parentheses becomes quite manageable, leading to the final answer of \displaystyle 2^9\cdot 3

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