Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 14 Jul 2012
Posts: 8
Location: Canada
Concentration: Marketing, Entrepreneurship
WE: Sales (Other)

If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
Updated on: 19 Mar 2013, 12:54
Question Stats:
65% (01:07) correct 35% (00:52) wrong based on 562 sessions
HideShow timer Statistics
If xy > 0 and yz < 0, which of the following must be negative: A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2)
Official Answer and Stats are available only to registered users. Register/ Login.
Originally posted by GMAThirst on 19 Mar 2013, 12:42.
Last edited by Bunuel on 19 Mar 2013, 12:54, edited 2 times in total.
Renamed the topic, edited the question and the tags.



Math Expert
Joined: 02 Sep 2009
Posts: 46291

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
19 Mar 2013, 12:57



Manager
Joined: 04 Oct 2011
Posts: 201
Location: India
Concentration: Entrepreneurship, International Business
GPA: 3

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
19 Mar 2013, 18:05
GMAThirst wrote: If xy > 0 and yz < 0, which of the following must be negative:
A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2) xy > 0 ++ (or)  yz < 0 + (or) + Remember Square of any number is always +ve. so we can remove all squares A. xyz there is a chance for + so may be +B. xy ++ or  C. xz if x is + then z should be  and vice versa D. x may be + or E. +ve
_________________
GMAT  Practice, Patience, Persistence Kudos if u like



Intern
Joined: 14 Jul 2012
Posts: 8
Location: Canada
Concentration: Marketing, Entrepreneurship
WE: Sales (Other)

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
20 Mar 2013, 06:39
Hi, sorry to bother again, but I still didn't understand either of the explanations.....
I saw a long way in the book to solve it but I didn't get how both of you were able to solve it quick in that manner.
Thanks.



Math Expert
Joined: 02 Sep 2009
Posts: 46291

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
20 Mar 2013, 06:43



Intern
Joined: 14 Jul 2012
Posts: 8
Location: Canada
Concentration: Marketing, Entrepreneurship
WE: Sales (Other)

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
20 Mar 2013, 06:48
Hey Banuel,
Thanks it's much clearer now. Also, I'll make sure to follow the GMAT Rules for posting



Director
Joined: 03 Aug 2012
Posts: 829
Concentration: General Management, General Management
GMAT 1: 630 Q47 V29 GMAT 2: 680 Q50 V32
GPA: 3.7
WE: Information Technology (Investment Banking)

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
25 Jul 2013, 21:20
I follow the tables for these types of questions XY>0 => Both must be ve or both must be +ve. YZ<0 =>Both must be of opposite signs. X  Y  Z + +    + Evaluate all the options by this you will arrive at (C). Rgds, TGC !
_________________
Rgds, TGC! _____________________________________________________________________ I Assisted You => KUDOS Please _____________________________________________________________________________



Intern
Joined: 06 Jan 2013
Posts: 11
Location: United States
Concentration: Finance, Economics
GMAT Date: 11152013
GPA: 3.5
WE: Education (Education)

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
29 Aug 2013, 05:36
I also follow the table approach for these types of questions, as per the attached file. I set up the columns for x, y, and z, and check which combination of positive and negative values I need to satisfy the conditions given (xy>0 and yz<0), then I check each answer choice in turn. When actually doing these questions I wouldn't fill in the whole table (since the answer is C there is no point checking D and E), but for the sake of completeness I added them. Hope it helps a bit, I'm more visual so didn't either consider the algebraic approach given above!
Attachments
File comment: Solution table
Table.png [ 3.87 KiB  Viewed 7476 times ]



SVP
Joined: 06 Sep 2013
Posts: 1881
Concentration: Finance

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
05 Jan 2014, 08:14
GMAThirst wrote: If xy > 0 and yz < 0, which of the following must be negative:
A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2) If 'x' and 'y' have the same sign, and 'y' and 'z' have different signs, then it must follow that 'x' and 'z' have different sign Hence y^2 will always be positive and x*z will always be negative Thus C gives the correct answer Cheers! J



Director
Joined: 07 Aug 2011
Posts: 565
Concentration: International Business, Technology

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
15 Apr 2015, 03:59
GMAThirst wrote: If xy > 0 and yz < 0, which of the following must be negative:
A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2) from stem, x and y have same sign and z is just opposite to x and y . clear C .
_________________
Thanks, Lucky
_______________________________________________________ Kindly press the to appreciate my post !!



Director
Status: Professional GMAT Tutor
Affiliations: AB, cum laude, Harvard University (Class of '02)
Joined: 10 Jul 2015
Posts: 646
Location: United States (CA)
Age: 38
GMAT 1: 770 Q47 V48 GMAT 2: 730 Q44 V47 GMAT 3: 750 Q50 V42
GRE 1: 337 Q168 V169
WE: Education (Education)

If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
05 May 2016, 18:30
Attached is a visual that should help.
Attachments
Screen Shot 20160505 at 6.44.19 PM.png [ 141.98 KiB  Viewed 4084 times ]
_________________
Harvard grad and 99% GMAT scorer, offering expert, private GMAT tutoring and coaching, both inperson (San Diego, CA, USA) and online worldwide, since 2002.
One of the only known humans to have taken the GMAT 5 times and scored in the 700s every time (700, 710, 730, 750, 770), including verified section scores of Q50 / V47, as well as personal bests of 8/8 IR (2 times), 6/6 AWA (4 times), 50/51Q and 48/51V (1 question wrong).
You can download my official testtaker score report (all scores within the last 5 years) directly from the Pearson Vue website: https://tinyurl.com/y8zh6qby Date of Birth: 09 December 1979.
GMAT Action Plan and Free EBook  McElroy Tutoring



Manager
Joined: 26 Mar 2017
Posts: 145

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
12 May 2017, 03:20
since xy>0 (pos) and yz<0 (neg) > xy (neg) * yz (pos) must be negative rewrite xy (neg) * yz (pos) > x(y^2)z
_________________
I hate long and complicated explanations!



Manager
Joined: 21 Jun 2017
Posts: 78

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
23 Aug 2017, 20:13
GMAThirst wrote: If xy > 0 and yz < 0, which of the following must be negative:
A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2) I enjoyed solving this problem. After solving it, It was also a pleasure seeing it categorized as Medium and a 600 question.  Starting with the givens: Given XY > 0 this given should be interpreted as Either both X and Y are positive or Negative. For the product of two like signs always yields a positive. Given YZ < 0 this given should be interpreted as either Y or Z as positive or negative. For the product of two different signs always yields a negative.Considering the implications of the givens, this problem branches off in two directions: the first is Y is negative; therefore, X is negative and Z is positive. And the second, Both X and Y are positive, while Z is negativeThis problem asks for a MUST solution, so our two branches need to overlap the same answer. If X and Y =  Z = + then (A) (B) (E) is eliminated, leaving us with (C) and (D) as possible Answers If X and Y = + Z =  then (B)(D)(E) is eliminated, leaving us with (A) and (C) as possible answers. Since the only overlapping solution to our two branches is (C), (C) must be the answer



Senior Manager
Joined: 29 Jun 2017
Posts: 499
GPA: 4
WE: Engineering (Transportation)

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
23 Aug 2017, 22:15
Clearly C is the Answer. See the pic, solution is attached,
Attachments
IMG_5420.JPG [ 1.63 MiB  Viewed 1658 times ]
_________________
Give Kudos for correct answer and/or if you like the solution.



Director
Joined: 04 Dec 2015
Posts: 700
Location: India
Concentration: Technology, Strategy
WE: Information Technology (Consulting)

If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
27 Aug 2017, 18:11
GMAThirst wrote: If xy > 0 and yz < 0, which of the following must be negative:
A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2) \(xy>0\)  (Both \(x\) and \(y\) are either positive or negative. ie; \(x\) and \(y\) have same signs) \(yz<0\)  (\(y\) and \(z\) have different signs) Lets check the options. Case one : \(x\) and \(y\) are positive and \(z\) is negative. Square of negative is positive. A. \(xyz = (positive)(positive)(negative) = negative\) B. \(xy(z^2) = (positive)(positive)(negative^2) = positive\) C. \(x(y^2)z = (positive)(positive^2)(negative) = negative\) D. \(x(y^2)(z^2) = (positive)(positive^2)(negative^2) = positive\) E. \((x^2)(y^2)(z^2) = (positive^2)(positive^2)(negative^2) = positive\) Case two: \(x\) and \(y\) are negative and \(z\) is positive. Square of negative is positive. A. \(xyz = (negative)(negative)(positive) = positive\) B. \(xy(z^2) = (negative)(negative)(positive^2) = positive\) C. \(x(y^2)z = (negative)(negative^2)(positive) = negative\) D. \(x(y^2)(z^2) = (negative)(negative^2)(positive^2) = negative\) E. \((x^2)(y^2)(z^2) = (negative^2)(negative^2)(positive^2) = positive\) Question is asking which of the following "must be" negative. From both the cases, we get, C is negative. Hence Answer C. Answer (C)...



Target Test Prep Representative
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2570

Re: If xy > 0 and yz < 0, which of the following must be negativ [#permalink]
Show Tags
31 Aug 2017, 10:24
GMAThirst wrote: If xy > 0 and yz < 0, which of the following must be negative:
A. xyz B. xy(z^2) C. x(y^2)z D. x(y^2)(z^2) E. (x^2)(y^2)(z^2) SInce xy > 0: x = pos and y = pos OR x = neg and y = neg SInce yz < 0: y = neg and z = pos OR y = pos and z = neg Thus, we have two scenarios: 1) x = pos, y = pos, and z = neg 2) x = neg, y = neg, and z = pos Since y^2 is always positive regardless of whether y is positive or negative, we see that the product of x and z will always be negative, and thus x(y^2)z will always be negative. Answer: C
_________________
Jeffery Miller
Head of GMAT Instruction
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions




Re: If xy > 0 and yz < 0, which of the following must be negativ
[#permalink]
31 Aug 2017, 10:24






