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Math Expert
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Re M2534
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16 Sep 2014, 01:24



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Re: M2534
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17 Nov 2014, 04:54
Bunuel wrote: Official Solution:
Inequality \(x^7*y^2*z^3 \gt 0\) to be true \(x\) and \(z\) must be either both positive or both negative (in order \(x^7*z^3\) to be positive) AND \(y\) must not be zero (in order \(x^7*y^2*z^3\) not to equal to zero). (1) \(yz \lt 0\). This statement implies that \(y \neq 0\). Don't know about \(x\) and \(z\). Not sufficient. (2) \(xz \gt 0\). This statement implies that \(x\) and \(z\) are either both positive or both negative. Don't know about \(y\). Not sufficient. (1)+(2) Sufficient.
Answer: C Hi Bunuel, for (2) don't we know that y is always positive given it's raised to the power of 2 (and there's no imaginery numbers on the GMAT)? Therefore, if y is always positive, then (2) is sufficient?



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Re: M2534
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17 Nov 2014, 06:19
illusion10 wrote: Bunuel wrote: Official Solution:
Inequality \(x^7*y^2*z^3 \gt 0\) to be true \(x\) and \(z\) must be either both positive or both negative (in order \(x^7*z^3\) to be positive) AND \(y\) must not be zero (in order \(x^7*y^2*z^3\) not to equal to zero). (1) \(yz \lt 0\). This statement implies that \(y \neq 0\). Don't know about \(x\) and \(z\). Not sufficient. (2) \(xz \gt 0\). This statement implies that \(x\) and \(z\) are either both positive or both negative. Don't know about \(y\). Not sufficient. (1)+(2) Sufficient.
Answer: C Hi Bunuel, for (2) don't we know that y is always positive given it's raised to the power of 2 (and there's no imaginery numbers on the GMAT)? Therefore, if y is always positive, then (2) is sufficient? Yes I agree, I think the answer must be B, because with the information given the answer is always > 0



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Re: M2534
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17 Nov 2014, 06:32
illusion10 wrote: Bunuel wrote: Official Solution:
Inequality \(x^7*y^2*z^3 \gt 0\) to be true \(x\) and \(z\) must be either both positive or both negative (in order \(x^7*z^3\) to be positive) AND \(y\) must not be zero (in order \(x^7*y^2*z^3\) not to equal to zero). (1) \(yz \lt 0\). This statement implies that \(y \neq 0\). Don't know about \(x\) and \(z\). Not sufficient. (2) \(xz \gt 0\). This statement implies that \(x\) and \(z\) are either both positive or both negative. Don't know about \(y\). Not sufficient. (1)+(2) Sufficient.
Answer: C Hi Bunuel, for (2) don't we know that y is always positive given it's raised to the power of 2 (and there's no imaginery numbers on the GMAT)? Therefore, if y is always positive, then (2) is sufficient? For statement (2), Y could be zero also, in that case \(x^7*y^2*z^3 \gt 0\) will not hold true.



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Re: M2534
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17 Nov 2014, 06:35
gbascurs wrote: illusion10 wrote: Bunuel wrote: Official Solution:
Inequality \(x^7*y^2*z^3 \gt 0\) to be true \(x\) and \(z\) must be either both positive or both negative (in order \(x^7*z^3\) to be positive) AND \(y\) must not be zero (in order \(x^7*y^2*z^3\) not to equal to zero). (1) \(yz \lt 0\). This statement implies that \(y \neq 0\). Don't know about \(x\) and \(z\). Not sufficient. (2) \(xz \gt 0\). This statement implies that \(x\) and \(z\) are either both positive or both negative. Don't know about \(y\). Not sufficient. (1)+(2) Sufficient.
Answer: C Hi Bunuel, for (2) don't we know that y is always positive given it's raised to the power of 2 (and there's no imaginery numbers on the GMAT)? Therefore, if y is always positive, then (2) is sufficient? Yes I agree, I think the answer must be B, because with the information given the answer is always > 0 I saw what is the problem with B, Y can be 0 or not.....



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Re: M2534
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19 Nov 2014, 03:51
chetan86 wrote: illusion10 wrote: Bunuel wrote: Official Solution:
Inequality \(x^7*y^2*z^3 \gt 0\) to be true \(x\) and \(z\) must be either both positive or both negative (in order \(x^7*z^3\) to be positive) AND \(y\) must not be zero (in order \(x^7*y^2*z^3\) not to equal to zero). (1) \(yz \lt 0\). This statement implies that \(y \neq 0\). Don't know about \(x\) and \(z\). Not sufficient. (2) \(xz \gt 0\). This statement implies that \(x\) and \(z\) are either both positive or both negative. Don't know about \(y\). Not sufficient. (1)+(2) Sufficient.
Answer: C Hi Bunuel, for (2) don't we know that y is always positive given it's raised to the power of 2 (and there's no imaginery numbers on the GMAT)? Therefore, if y is always positive, then (2) is sufficient? For statement (2), Y could be zero also, in that case \(x^7*y^2*z^3 \gt 0\) will not hold true. Thanks, definitely got caught out on that trap!



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Re: M2534
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31 Dec 2014, 02:47
I think the answer should be B. Given that Y is squared, it can be inferred that the middle Y term is POSITIVE. If both X and Z are negative, it yields a final positive number. Likewise, if both X and Z are positive, it yields a final positive number as well.



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31 Dec 2014, 04:54



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Re: M2534
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15 Feb 2015, 05:08
I just love this kind of GMAT questions. They know after reading (A) you will assume you know what "y" is. Genious!
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Re: M2534
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09 Apr 2015, 07:26
I got this question in the GMATClub test and picked B as the answer. Should have considered y could also be zero.
Really nice question, thank you!



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Re M2534
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04 Nov 2015, 16:28
I think this is a highquality question and the explanation isn't clear enough, please elaborate. There's not a clear explanation why c is sufficient can you please show with numbers ?



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Re M2534
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22 Aug 2016, 04:30
I think this is a highquality question and I agree with explanation.



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Re: M2534
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13 Jul 2018, 07:09
Bunuel wrote: Official Solution:
Inequality \(x^7*y^2*z^3 \gt 0\) to be true \(x\) and \(z\) must be either both positive or both negative (in order \(x^7*z^3\) to be positive) AND \(y\) must not be zero (in order \(x^7*y^2*z^3\) not to equal to zero). (1) \(yz \lt 0\). This statement implies that \(y \neq 0\). Don't know about \(x\) and \(z\). Not sufficient. (2) \(xz \gt 0\). This statement implies that \(x\) and \(z\) are either both positive or both negative. Don't know about \(y\): if \(y=0\), then the expression is not positive it's equal 0 . Not sufficient. Notice that if \(\) (1)+(2) Sufficient.
Answer: C This is a super sneaky one because generally I think you'll see xyz =/= 0, whereas here it's not present and the testtaker will still assume it.










