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M60-09

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Math Revolution GMAT Instructor
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V
Joined: 16 Aug 2015
Posts: 7462
GMAT 1: 760 Q51 V42
GPA: 3.82
M60-09  [#permalink]

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New post 11 Jun 2018, 03:15
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

60% (01:00) correct 40% (01:03) wrong based on 10 sessions

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If \(w^2 x^3 y^4 z^5 < 0\), is \(xyz > 0\)?

1) \(x < 0\)

2) \(y < 0\)

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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
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Math Revolution GMAT Instructor
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Joined: 16 Aug 2015
Posts: 7462
GMAT 1: 760 Q51 V42
GPA: 3.82
Re M60-09  [#permalink]

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New post 11 Jun 2018, 03:15
1
Official Solution:



Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question, and then recheck the question.

Modifying the original condition and question:

The original condition \(w^2 x^3 y^4 z^5 < 0\) is equivalent to \(xz < 0\) since we can ignore terms with even exponents in this type of inequality (they are always positive).



Under the modified condition \(xz < 0\), the question, 'is \(xyz > 0\)?' is equivalent to 'is \(y < 0\)?', which is the same as condition 2).



Since condition 1) tells us nothing about the sign of y, the answer is B.



Therefore, the answer is B.

Answer: B
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MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
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Re M60-09  [#permalink]

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New post 31 Mar 2019, 08:09
I think this is a high-quality question and I agree with explanation.
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Joined: 23 May 2019
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Re M60-09  [#permalink]

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New post 24 May 2019, 02:54
I think this is a poor-quality question. I do not understand how the answer to the question is B.
I know that given that the powers are even, the outcome will be positive. But, I do not know how to go from there.
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Re M60-09   [#permalink] 24 May 2019, 02:54
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