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

 It is currently 25 Oct 2016, 06:55

Today's Live Q&A Sessions:

UCLA Anderson Adcom Chat at 8AM Pacific | LBS / INSEAD / HEC Paris Chat at 9AM Pacific  | Join Chat Room to Participate

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

M21-30 Mistake?

Author Message
Intern
Joined: 05 Nov 2012
Posts: 4
Followers: 0

Kudos [?]: 1 [0], given: 2

Show Tags

19 Feb 2013, 04:01
1
This post was
BOOKMARKED
Is $$x^2*y^3*z>0?$$

(1) yz>0

(2) xz<0

The official answer from Gmat Club is C.

I strongly think the correct answer is A and here is why:

From statement 1 y & z have the same sign wither both - or both +. This mean that the part of the equation given $$y^3*z$$ is positive. And since $$x^$$ has to be positive we can conclude that statement 1 is sufficient.

What do you think?

Cheers
Math Expert
Joined: 02 Sep 2009
Posts: 35284
Followers: 6637

Kudos [?]: 85650 [2] , given: 10241

Show Tags

19 Feb 2013, 04:28
2
KUDOS
Expert's post
wieseljonas wrote:
Is $$x^2*y^3*z>0?$$

(1) yz>0

(2) xz<0

The official answer from Gmat Club is C.

I strongly think the correct answer is A and here is why:

From statement 1 y & z have the same sign wither both - or both +. This mean that the part of the equation given $$y^3*z$$ is positive. And since $$x^$$ has to be positive we can conclude that statement 1 is sufficient.

What do you think?

Cheers

Is $$x^2*y^3*z>0$$?

Inequality $$x^2*y^3*z>0$$ to be true:
1. $$y$$ and $$z$$ must be either both positive or both negative, so they must have the same sign (in this case $$y^3*z$$ will be positive);
AND
2. $$x$$ must not be zero (in this case $$x^2$$ will be positive).

(1) $$yz>0$$. From this statement it follows that $$y$$ and $$z$$ are either both positive or both negative, so the first condition is satisfied. But we don't know about $$x$$ (the second condition). Not sufficient.

(2) $$xz<0$$. From this statement it follows that $$x\neq{0}$$, so the second condition is satisfied. Don't know about the signs of $$y$$ and $$z$$ (the first condition). Not sufficient.

(1)+(2) Both conditions are satisfied. Sufficient.

Similar questions to practice:
is-x-2-y-5-z-0-1-xz-y-0-2-y-z-98341.html
is-x-7-y-2-z-3-0-1-yz-0-2-xz-127692.html
m21-q30-96613.html

Hope it helps.
_________________
Intern
Joined: 05 Nov 2012
Posts: 4
Followers: 0

Kudos [?]: 1 [0], given: 2

Show Tags

19 Feb 2013, 04:30
Ok thanks.

It's the x must not be zero that I missed! Thanks you!
Re: M21-30 Mistake?   [#permalink] 19 Feb 2013, 04:30
Display posts from previous: Sort by

M21-30 Mistake?

Moderator: Bunuel

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.