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Expert Post
Math Revolution GMAT Instructor
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D
Joined: 16 Aug 2015
Posts: 4880
GPA: 3.82
r=? [#permalink]

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New post 23 May 2017, 01:25
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

63% (00:38) correct 38% (00:43) wrong based on 40 sessions

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r=?

1) \(r^3-r^2=0\)
2) \(r=-r\)
[Reveal] Spoiler: OA

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Joined: 06 Jan 2015
Posts: 312
Location: India
Concentration: Operations, Finance
GPA: 3.35
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Re: r=? [#permalink]

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New post 23 May 2017, 02:24
MathRevolution wrote:
r=?

1) \(r^3-r^2=0\)
2) \(r=-r\)


1) \(r^3-r^2=0\)=\(r^2(r-1)=0\)
r=0 or 1

2) \(r=-r\) => 2r=0 i,e r=0

Hence B
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Expert Post
Math Revolution GMAT Instructor
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D
Joined: 16 Aug 2015
Posts: 4880
GPA: 3.82
Re: r=? [#permalink]

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New post 25 May 2017, 00:16
==> In the original condition, there is 1 variable (r), and in order to match the number of variables to the number of equations, there must be 1 equation. Since there is 1 for con 1) and 1 for con 2), D is most likely to be the answer.
For con 1), from r2(r-1)=0, you get r=0,1, hence it is not unique and not sufficient.
For con 2), from 2r=0, you get r=0, hence it is unique and sufficient. Therefore, the answer is B.

Answer: B
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Re: r=?   [#permalink] 25 May 2017, 00:16
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