BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

GMAT Set 12

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Data Sufficiency |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Wed Feb 25, 2015 6:17 am
Abhijit K wrote:If s�v³x� < 0, is svx < 0?
(1) v < 0
(2) x > 0
Since s�v³x� < 0, svx≠0.
Implication:
If s, v or x is raised to ANY EVEN POWER, the result will be POSITIVE.

Implication:
Each side of s�v³x� < 0 can safely be divided by any even power of s, v, or x.
Thus:
(s�v³x�)/(s�v²x�) < 0/(s�v²x�)
vx < 0.

Question stem: Is svx < 0?
Since vx < 0, svx < 0 only if s>0.
Question stem, rephrased:
Is s>0?

Even when the statements are combined, it is possible that s<0 or s>0.

The correct answer is E.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pm
Location: Palo Alto, CA
Thanked: 2867 times
Followed by:511 members
GMAT Score:800

by [email protected] » Wed Feb 25, 2015 12:59 pm
Hi Abhijit K,

This DS question is loaded with Number Property rules and you have to be thorough with your thinking to get the correct answer.

First, since s�v³x� < 0 we have to think about what S, V and X COULD be....

Since the product is less than 0, NONE of those variables can equal 0.

s� will always be positive, but S COULD be positive or negative

v³ will be positive IF V is positive.
v³ will be negative IF V is negative

x� will be positive IF X is positive
x� will be negative IF X is negative

So, knowing that s�v³x� < 0, that means....

We don't know whether S is positive or negative
Between V and X, one is positive and one is negative.

(+)(+)(-) = less than 0
(+)(-)(+) = less than 0

Knowing all of this, we can now work on the question itself: Is (S)(V)(X) < 0? This is a YES/NO question.

Fact 1: V < 0

Knowing that V is negative, we also know that X is positive. HOWEVER, we don't know whether S is positive OR negative...

IF....S is positive, we have (+)(-)(+) = negative and the answer to the question is YES.
IF....S is negative, we have (-)(-)(+) = negative and the answer to the question is NO.
Fact 1 is INSUFFICENT

Fact 2: X > 0

Here, we have the same situation that we had in Fact 1. We know that X is positive, so we know that V is negative, but we don't know about S. The same two examples in Fact 1 fit here as well.
Fact 2 is SUFFICIENT.

Combined, we know...
V < 0
X > 0
And all of the deductions that we made form the prompt itself.

We end up with the same 2 examples that we had before - one YES and one NO answer.
Combined, INSUFFICIENT.

Final Answer: E

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pm
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1268 members
GMAT Score:770

by Brent@GMATPrepNow » Thu Feb 26, 2015 10:25 am
The above solutions are great, so I won't delve into in the solution.
I just want to note that, at the heart of this question lie the following (important) properties:

Two important rules:

ODD exponents preserve the sign of the base.
So, (NEGATIVE)^(ODD integer) = NEGATIVE
and (POSITIVE)^(ODD integer) = POSITIVE

An EVEN exponent always yields a positive result (unless the base = 0)
So, (NEGATIVE)^(EVEN integer) = POSITIVE
and (POSITIVE)^(EVEN integer) = POSITIVE

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
Top
Post new topic Post Reply
• Page 1 of 1