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16 Sep 2014, 01:24
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16 Sep 2014, 01:24
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Official Solution:
Is \(x^7y^2z^3 > 0\) ?
In order for \(x^7y^2z^3 > 0\) to be true, the following conditions must be met:
1. \(y\) cannot be zero. If \(y = 0\), then \(x^7y^2z^3 \) will equal 0, not greater than it.
AND
2. \(x\) and \(z\) must be either both positive or both negative. If \(x\) and \(z\) have different signs (or if either of them is 0), then \(x^7z^3 \) will be negative (or 0), not positive as required.
(1) \(yz < 0\).
This statement implies that \(y \neq 0\), so the first condition is satisfied. However, we don't have information about the signs of \(x\) and \(z\). Not sufficient.
(2) \(xz > 0\).
This statement implies that \(x\) and \(z\) are either both positive or both negative. So, the second condition is met. However, we don't have information about \(y\); if \(y=0\), then the expression is not positive, but equal to 0. Not sufficient.
(1)+(2) Both conditions, \(y\) not being 0 and \(x\) and \(z\) having the same sign, are satisfied. Therefore, \(x^7y^2z^3 > 0\). Sufficient.
Answer: C
Is \(x^7y^2z^3 > 0\) ?
In order for \(x^7y^2z^3 > 0\) to be true, the following conditions must be met:
1. \(y\) cannot be zero. If \(y = 0\), then \(x^7y^2z^3 \) will equal 0, not greater than it.
AND
2. \(x\) and \(z\) must be either both positive or both negative. If \(x\) and \(z\) have different signs (or if either of them is 0), then \(x^7z^3 \) will be negative (or 0), not positive as required.
(1) \(yz < 0\).
This statement implies that \(y \neq 0\), so the first condition is satisfied. However, we don't have information about the signs of \(x\) and \(z\). Not sufficient.
(2) \(xz > 0\).
This statement implies that \(x\) and \(z\) are either both positive or both negative. So, the second condition is met. However, we don't have information about \(y\); if \(y=0\), then the expression is not positive, but equal to 0. Not sufficient.
(1)+(2) Both conditions, \(y\) not being 0 and \(x\) and \(z\) having the same sign, are satisfied. Therefore, \(x^7y^2z^3 > 0\). Sufficient.
Answer: C
General Discussion
bgpower
Joined: 03 Aug 2011
Last visit: 14 Mar 2017
Posts: 267
Given Kudos: 916
Concentration: Strategy, Finance
Schools: CBS '19 (WL) HBS '19 (D) Haas '19 (A) Kellogg '19 Stanford '19 (D) Wharton '19 (D) Booth '19 (A) Sloan '19 (D)
GMAT 1: 640 Q44 V34
GMAT 2: 700 Q42 V44
GMAT 3: 680 Q44 V39
GMAT 4: 740 Q49 V41
GPA: 3.7
WE:Project Management (Energy)
Products:
Schools: CBS '19 (WL) HBS '19 (D) Haas '19 (A) Kellogg '19 Stanford '19 (D) Wharton '19 (D) Booth '19 (A) Sloan '19 (D)
GMAT 4: 740 Q49 V41
Posts: 267
15 Feb 2015, 05:08
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I just love this kind of GMAT questions. They know after reading (A) you will assume you know what "y" is. Genious!
