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GRE Prep Club Legend  Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 105

Kudos [?]: 1783 , given: 397

–(x)3 = 64 [#permalink]
Expert's post 00:00

Question Stats: 93% (00:25) correct 6% (00:41) wrong based on 29 sessions
$$-(x)^3 = 64$$

 Quantity A Quantity B $$x^4$$ $$x^5$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

_________________

Sandy
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Director Joined: 20 Apr 2016
Posts: 828
WE: Engineering (Energy and Utilities)
Followers: 11

Kudos [?]: 606 , given: 124

Re: –(x)3 = 64 [#permalink]
sandy wrote:
$$-(x)^3 = 64$$

 Quantity A Quantity B $$x^4$$ $$x^5$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.

Here:

$$-(x)^3 = 64$$

or -x = 4
or x = -4

In Quantity A : $$x^4$$= $$(-4)^4$$ = 256

In Quantity B: $$x^5$$= $$(-4)^5$$ = -1024

Hence Quantity A > Quantity B
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Intern Joined: 15 May 2018
Posts: 38
Followers: 0

Kudos [?]: 5 , given: 1

Re: –(x)3 = 64 [#permalink]
sandy wrote:
$$-(x)^3 = 64$$

 Quantity A Quantity B $$x^4$$ $$x^5$$

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.

My Answer is A
GRE Prep Club Legend  Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 105

Kudos [?]: 1783 , given: 397

Re: –(x)3 = 64 [#permalink]
Expert's post
Explanation

First, solve for x:

$$-(x)^3 = 64$$
$$(x)^3 = -64$$

The GRE calculator will not do a cube root. As a result, cube roots on the GRE tend to be quite small and easy to puzzle out. What number times itself three times equals –64? The answer is x = –4.

Since x is negative, Quantity A is positive (a negative number times itself four times is positive) and Quantity B is negative (a negative number times itself five times is negative). No further calculations are needed to conclude that Quantity A is greater.

Notice that solving for the value of x here was not strictly necessary. Knowing that the cube root of a negative number is negative gives you all the information you need to solve.
_________________

Sandy
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Try our free Online GRE Test Re: –(x)3 = 64   [#permalink] 16 Jul 2018, 06:57
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