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–(x)3 = 64

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GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1653 [0], given: 396

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–(x)3 = 64 [#permalink] New post 23 Jun 2018, 12:03
Expert's post
00:00

Question Stats:

91% (00:23) correct 8% (00:41) wrong based on 24 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

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Sandy
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Director
Director
Joined: 20 Apr 2016
Posts: 756
Followers: 6

Kudos [?]: 511 [0], given: 94

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Re: –(x)3 = 64 [#permalink] New post 29 Jun 2018, 06:04
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
Intern
Joined: 15 May 2018
Posts: 39
Followers: 0

Kudos [?]: 5 [0], given: 1

Re: –(x)3 = 64 [#permalink] New post 09 Jul 2018, 18:41
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
GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1653 [0], given: 396

CAT Tests
Re: –(x)3 = 64 [#permalink] New post 16 Jul 2018, 06:57
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.
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Re: –(x)3 = 64   [#permalink] 16 Jul 2018, 06:57
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