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M25-34

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M25-34  [#permalink]

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New post 16 Sep 2014, 01:24
3
19
00:00
A
B
C
D
E

Difficulty:

  95% (hard)

Question Stats:

28% (01:01) correct 72% (00:54) wrong based on 460 sessions

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Re M25-34  [#permalink]

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New post 16 Sep 2014, 01:24
4
9
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
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Re: M25-34  [#permalink]

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New post 17 Nov 2014, 04:54
1
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: M25-34  [#permalink]

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New post 17 Nov 2014, 06:19
1
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: M25-34  [#permalink]

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New post 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: M25-34  [#permalink]

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New post 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: M25-34  [#permalink]

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New post 19 Nov 2014, 03:51
1
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: M25-34  [#permalink]

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New post 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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Re: M25-34  [#permalink]

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New post 31 Dec 2014, 04:54
meisin123 wrote:
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.


Please read the whole thread before posting. Thank you.

y^2 is not positive, it's non-negative, so it CAN be 0.
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Re: M25-34  [#permalink]

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New post 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!
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Re: M25-34  [#permalink]

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New post 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 M25-34  [#permalink]

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New post 04 Nov 2015, 16:28
I think this is a high-quality 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 M25-34  [#permalink]

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New post 22 Aug 2016, 04:30
I think this is a high-quality question and I agree with explanation.
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Re: M25-34  [#permalink]

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New post 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 test-taker will still assume it.
Re: M25-34 &nbs [#permalink] 13 Jul 2018, 07:09
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