Jul 21 07:00 AM PDT  09:00 AM PDT Attend this webinar to learn a structured approach to solve 700+ Number Properties question in less than 2 minutes Jul 20 07:00 AM PDT  09:00 AM PDT Attend this webinar and master GMAT SC in 10 days by learning how meaning and logic can help you tackle 700+ level SC questions with ease. Jul 26 08:00 AM PDT  09:00 AM PDT The Competition Continues  Game of Timers is a teambased competition based on solving GMAT questions to win epic prizes! Starting July 1st, compete to win prep materials while studying for GMAT! Registration is Open! Ends July 26th Jul 27 07:00 AM PDT  09:00 AM PDT Learn reading strategies that can help even nonvoracious reader to master GMAT RC
Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 56304

Question Stats:
27% (01:26) correct 73% (01:11) wrong based on 375 sessions
HideShow timer Statistics
Is \((x^7)(y^2)(z^3) \gt 0\) ? (1) \(yz \lt 0\) (2) \(xz \gt 0\)
Official Answer and Stats are available only to registered users. Register/ Login.
_________________



Math Expert
Joined: 02 Sep 2009
Posts: 56304

Re M2534
[#permalink]
Show Tags
16 Sep 2014, 01:24
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
_________________



Intern
Joined: 23 Oct 2014
Posts: 4

Re: M2534
[#permalink]
Show Tags
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?



Intern
Joined: 25 Dec 2012
Posts: 16

Re: M2534
[#permalink]
Show Tags
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



Manager
Joined: 17 Oct 2012
Posts: 61
Location: India
Concentration: Strategy, Finance
WE: Information Technology (Computer Software)

Re: M2534
[#permalink]
Show Tags
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.



Intern
Joined: 25 Dec 2012
Posts: 16

Re: M2534
[#permalink]
Show Tags
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.....



Intern
Joined: 23 Oct 2014
Posts: 4

Re: M2534
[#permalink]
Show Tags
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!



Intern
Joined: 12 Oct 2014
Posts: 1

Re: M2534
[#permalink]
Show Tags
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.



Math Expert
Joined: 02 Sep 2009
Posts: 56304

Re: M2534
[#permalink]
Show Tags
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 nonnegative, so it CAN be 0.
_________________



Current Student
Joined: 03 Aug 2011
Posts: 280
Concentration: Strategy, Finance
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 and Utilities)

Re: M2534
[#permalink]
Show Tags
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!
_________________
Thank you very much for reading this post till the end! Kudos?



Intern
Joined: 15 Aug 2014
Posts: 7

Re: M2534
[#permalink]
Show Tags
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!



Manager
Joined: 28 Dec 2013
Posts: 68

Re M2534
[#permalink]
Show Tags
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 ?



Senior Manager
Joined: 31 Mar 2016
Posts: 376
Location: India
Concentration: Operations, Finance
GPA: 3.8
WE: Operations (Commercial Banking)

Re M2534
[#permalink]
Show Tags
22 Aug 2016, 04:30
I think this is a highquality question and I agree with explanation.



Intern
Joined: 12 Jan 2017
Posts: 34
Location: United States (NY)
GPA: 3.48

Re: M2534
[#permalink]
Show Tags
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.



Intern
Joined: 16 Jun 2018
Posts: 38
Location: India
GPA: 4

Re M2534
[#permalink]
Show Tags
11 Dec 2018, 11:18
I don't agree with the explanation. I think the answer should be B, because if at we consider the value of any of the variables x / y/ z as 0, then the question in itself will not hold true.



Math Expert
Joined: 02 Sep 2009
Posts: 56304

Re: M2534
[#permalink]
Show Tags
11 Dec 2018, 21:39
Sheetal15 wrote: I don't agree with the explanation. I think the answer should be B, because if at we consider the value of any of the variables x / y/ z as 0, then the question in itself will not hold true. The correct answer is C. For (2) if y = 0, (which does NOT contradict the second statement) then the expression (x^7∗y^2∗z^3) will not positive it will be 0. This is explained couple of times above.
_________________



Director
Joined: 14 Feb 2017
Posts: 724
Location: Australia
Concentration: Technology, Strategy
GMAT 1: 560 Q41 V26 GMAT 2: 550 Q43 V23 GMAT 3: 650 Q47 V33
GPA: 2.61
WE: Management Consulting (Consulting)

Re: M2534
[#permalink]
Show Tags
13 Jul 2019, 21:31
Its easy to see that if we know the signs of x and z we can determine whether the question is > 0, PROVIDED Y =/= 0 Y= 0 must be tested here. Statement 1 indicates that Y cannot equal 0, but doesn't indicate the signs of x, therefore Insufficient Statement 2 indicates that xz> 0, but we don't know if y=0. If y=0 then (positive)*0^even exponent is not greater than 0 If y is not equal to zero than (positive)*(y)^even exponent > 0 I tripped on this mistake myself. Making a note for retention.
_________________
Goal: Q49, V41
+1 Kudos if you like my post pls!










