Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 23 May 2013, 06:50

# confusing Question from GMAT Prep test

Author Message
TAGS:
Manager
Status: GMAT Preperation
Joined: 04 Feb 2010
Posts: 105
Schools: HBS, Tuck
Followers: 1

Kudos [?]: 2 [0], given: 15

confusing Question from GMAT Prep test [#permalink]  26 Aug 2010, 00:20
00:00

Question Stats:

60% (01:16) correct 40% (02:03) wrong based on 0 sessions
If XY+Z=X(Y+Z), which of the following must be true ?

A) X=0 and Z=0
B) X=1 AND Y=1
C) Y=1 AND Z=0
D) X=1 OR Y=0
E) X=1 OR Z=0
[Reveal] Spoiler: OA

Last edited by vanidhar on 26 Aug 2010, 00:26, edited 1 time in total.
Director
Status: Apply - Last Chance
Affiliations: IIT, Purdue, PhD, TauBetaPi
Joined: 18 Jul 2010
Posts: 694
Schools: Wharton, Sloan, Chicago, Haas
WE 1: 8 years in Oil&Gas
Followers: 13

Kudos [?]: 50 [0], given: 15

Re: confusing Question from GMAT Prep test [#permalink]  26 Aug 2010, 00:23
You have got the options wrong. Z(X-1) = 0 means Z=0 or X=1.
_________________

Consider kudos, they are good for health

Manager
Status: GMAT Preperation
Joined: 04 Feb 2010
Posts: 105
Schools: HBS, Tuck
Followers: 1

Kudos [?]: 2 [0], given: 15

Re: confusing Question from GMAT Prep test [#permalink]  26 Aug 2010, 00:28
whats the method .. cause for me even x=0 and z=0 made sense when i put them into the eq
Director
Status: Apply - Last Chance
Affiliations: IIT, Purdue, PhD, TauBetaPi
Joined: 18 Jul 2010
Posts: 694
Schools: Wharton, Sloan, Chicago, Haas
WE 1: 8 years in Oil&Gas
Followers: 13

Kudos [?]: 50 [0], given: 15

Re: confusing Question from GMAT Prep test [#permalink]  26 Aug 2010, 02:00
XY+Z = XY +ZX
Cancel XY
Z=ZX
Z(X-1)=0
so Z=0 or X=1
_________________

Consider kudos, they are good for health

GMAT Club team member
Joined: 02 Sep 2009
Posts: 11583
Followers: 1797

Kudos [?]: 9581 [0], given: 826

Re: confusing Question from GMAT Prep test [#permalink]  26 Aug 2010, 05:24
vanidhar wrote:
If XY+Z=X(Y+Z), which of the following must be true ?

A) X=0 AND Z=0
B) X=1 AND Y=1
C) Y=1 AND Z=0
D) X=1 OR Y=0
E) X=1 OR Z=0

xy+z=x(y+z) --> xy+z=xy+xz --> xy cancels out --> xz-z=0 --> z(x-1)=0 --> either z=0 (in this case x can take ANY value) OR x=1 (in this case z can take ANY value).

To elaborate more:
As the expression with y cancels out, we can say that given expression xy+z=x(y+z) does not depend on value of y. Which means that y can take ANY value. So all answer choices which specify the exact value of y are wrong.

Next: "AND" in answer choices means that BOTH values must be true, but "OR" in answer choices means that EITHER value must be true.

Hope it helps.
_________________
Re: confusing Question from GMAT Prep test   [#permalink] 26 Aug 2010, 05:24
Similar topics Replies Last post
Similar
Topics:
GMAT PREP geometry question (confusing) 2 23 Dec 2006, 22:51
This are questions from GMAT Prep practice test. I do not 0 15 Jul 2007, 19:04
question from prep test 5 26 Oct 2009, 15:39
1 Help - questions from the official GMAT prep test 3 17 Aug 2010, 02:48
Gmat PREP test - oddly confused - symbolism maybe 2 31 Aug 2011, 19:26
Display posts from previous: Sort by