GRE Math : Exponential Operations

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #84 : Exponents

If \(\displaystyle 5^2 \times 5^n = 5^{12}\), what is the value of \(\displaystyle n\)?

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 14\)

\(\displaystyle 4\)

\(\displaystyle 24\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 10\)

Explanation:

Since the base is 5 for each term, we can say 2 + n =12.  Solve the equation for n by subtracting 2 from both sides to get n = 10.

Example Question #12 : Exponential Operations

Simplify \(\displaystyle x^{3}x^{6} + (x^{3})^{3} + x^{3}x^{2}x^{2}x^{2}\).

Possible Answers:

\(\displaystyle 3x^{9}\)

\(\displaystyle x^{18} + 2x^{9}\)

\(\displaystyle x^{27} + x^{18} + x^{9}\)

\(\displaystyle 2x^{9} + x^{27}\)

\(\displaystyle 3x^{3}\)

Correct answer:

\(\displaystyle 3x^{9}\)

Explanation:

Start by simplifying each individual term between the plus signs. We can add the exponents in \(\displaystyle x^3x^6\) and \(\displaystyle x^3x^2x^2x^2\) so each of those terms becomes \(\displaystyle x^9\). Then multiply the exponents in \(\displaystyle (x^3)^3\) so that term also becomes \(\displaystyle x^9\). Thus, we have simplified the expression to \(\displaystyle x^9 + x^9 + x^9\) which is \(\displaystyle 3x^{9}\).

Example Question #11 : Exponential Operations

Simplify \(\displaystyle x^{^{3}}x^{^{5}} - x^{^{2}} + (y^{^{2}})^{^{2}}\).

Possible Answers:

\(\displaystyle x^{15} - x^{2} + y^{4}\)

\(\displaystyle (xy)^{2}\)

\(\displaystyle x^{8} - x^{2} + y^{2}\)

\(\displaystyle x^{8} - x^{^{2}} + y^{4}\)

\(\displaystyle x^{6}+y^{4}\)

Correct answer:

\(\displaystyle x^{8} - x^{^{2}} + y^{4}\)

Explanation:

First, simplify \(\displaystyle x^{3}x^{5}\) by adding the exponents to get \(\displaystyle x^{8}\).

Then simplify \(\displaystyle (y^{2})^{2}\) by multiplying the exponents to get \(\displaystyle y^{4}\).

This gives us \(\displaystyle x^{8} - x^{^{2}} + y^{4}\). We cannot simplify any further.

Example Question #14 : Exponential Operations

If \(\displaystyle 3^4 \cdot 3^8 = 9^x\), what is the value of \(\displaystyle x?\)

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 16\)

\(\displaystyle \frac{4}{3}\)

\(\displaystyle 12\)

\(\displaystyle \frac{32}{9}\)

Correct answer:

\(\displaystyle 6\)

Explanation:

To attempt this problem, note that \(\displaystyle 3^2=(3)^2=9^1=9\).

Now note that when multiplying numbers, if the base is the same, we may add the exponents:

\(\displaystyle 3^4 \cdot 3^8 = 3^{4+8}=3^{12}\)

This can in turn be written in terms of nine as follows (recall above)

\(\displaystyle 3^{12}=9^{\frac{12}{2}}=9^6\)

\(\displaystyle 9^6=9^x\)

\(\displaystyle x=6\)

Example Question #12 : Exponential Operations

If \(\displaystyle (3^2\cdot3^5)^3=3^x\), what is the value of \(\displaystyle x?\)

Possible Answers:

\(\displaystyle 21\)

\(\displaystyle 7\)

\(\displaystyle 30\)

\(\displaystyle 10\)

\(\displaystyle 13\)

Correct answer:

\(\displaystyle 21\)

Explanation:

When dealing with exponenents, when multiplying two like bases together, add their exponents:

\(\displaystyle 3^2\cdot3^5=3^7\)

However, when an exponent appears outside of a parenthesis, or if the entire number itself is being raised by a power, multiply:

\(\displaystyle (3^7)^3=3^{7\cdot 3}=3^{21}\)

\(\displaystyle 3^{21}=3^{x}\)

\(\displaystyle x=21\)

Example Question #102 : Exponents

Simplify: 32 * (423 - 421)

Possible Answers:

4^4

3^3 * 4^21

3^21

None of the other answers

3^3 * 4^21 * 5

Correct answer:

3^3 * 4^21 * 5

Explanation:

Begin by noting that the group (423 - 421) has a common factor, namely 421.  You can treat this like any other constant or variable and factor it out.  That would give you: 421(42 - 1). Therefore, we know that:

32 * (423 - 421) = 32 * 421(42 - 1)

Now, 42 - 1 = 16 - 1 = 15 = 5 * 3.  Replace that in the original:

32 * 421(42 - 1) = 32 * 421(3 * 5)

Combining multiples withe same base, you get:

33 * 421 * 5

Example Question #13 : Exponential Operations

Quantitative Comparison

Quantity A: 64 – 32

Quantity B: 52 – 42

Possible Answers:

Quantity B is greater.

The two quantities are equal.

The relationship cannot be determined from the information given.

Quantity A is greater.

Correct answer:

Quantity A is greater.

Explanation:

We can solve this without actually doing the math. Let's look at 64 vs 52. 64 is clearly bigger. Now let's look at 32 vs 42. 32 is clearly smaller. Then, bigger – smaller is greater than smaller – bigger, so Quantity A is bigger.

Example Question #14 : Exponential Operations

\(\displaystyle a > 0\), and \(\displaystyle a\) is odd.

\(\displaystyle b > 1\)

Quantity A: \(\displaystyle (1-b)^a\)

Quantity B: \(\displaystyle (-b)^a\)

 

Possible Answers:

Quantity A is greater.

The two quantities are equal.

Quantity B is greater.

The relationship cannot be determined from the information given.

Correct answer:

Quantity A is greater.

Explanation:

The first thing to note is the relationship between (–b) and (1 – b):

 (–b) < (1 – b) because (–b) + 1 = (1 – b).

Now when b > 1, (1 – b) < 0 and –b < 0. Therefore (–b) < (1 – b) < 0.

Raising a negative number to an odd power produces another negative number.

Thus (–b)a < (1 – b)a < 0.

Example Question #22 : Exponents

(b * b* b7)1/2/(b3 * bx) = b5  

If b is not negative then x = ?

Possible Answers:

7

1

–2

–1

Correct answer:

–2

Explanation:

Simplifying the equation gives b6/(b3+x) = b5.  

In order to satisfy this case, x must be equal to –2.

Example Question #23 : Exponents

If〖7/8〗n= √(〖7/8〗5),then what is the value of n?

 

Possible Answers:

5/2

2/5

√5

1/5

25

Correct answer:

5/2

Explanation:

7/8 is being raised to the 5th power and to the 1/2 power at the same time. We multiply these to find n.

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