GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 23 Oct 2019, 06:15

### 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

# If w^2x^3y^4z^5<0, is xyz>0?

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 8033
GMAT 1: 760 Q51 V42
GPA: 3.82

### Show Tags

18 Jan 2018, 01:41
00:00

Difficulty:

65% (hard)

Question Stats:

55% (01:35) correct 45% (01:23) wrong based on 55 sessions

### HideShow timer Statistics

[GMAT math practice question]

If $$w^2x^3y^4z^5<0$$, is $$xyz>0$$?

$$1) x<0$$
$$2) y<0$$

_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 1 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" examPAL Representative Joined: 07 Dec 2017 Posts: 1153 Re: If w^2x^3y^4z^5<0, is xyz>0? [#permalink] ### Show Tags 18 Jan 2018, 05:08 MathRevolution wrote: [GMAT math practice question] If $$w^2x^3y^4z^5<0$$, is $$xyz>0$$? $$1) x<0$$ $$2) y<0$$ We're asked if a product is positive or negative so we'll look for an answer to do with number properties. This is a Logical approach. Since any even power is always positve, then w^2 and y^4 are positive. Then x^3 * z^5 is negative meaning that one of x,z must be negative and the other must be positive. So, x*z is negative. Therefore to know if xyz is positive or negative we need to know if y is positive or negative. (1) adds no information about y. Insufficient! (2) tells us that y is negative. Sufficient! (B) is our answrr. _________________ Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 8033 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: If w^2x^3y^4z^5<0, is xyz>0? [#permalink] ### Show Tags 21 Jan 2018, 18:35 => Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution. The first step of the VA (Variable Approach) method is to modify the original condition and the question, and then recheck the question. Modifying the original condition and question: The original condition $$w^2x^3y^4z^5<0$$ is equivalent to $$xz<0$$ since we can ignore terms with even exponents in this type of inequality (they are always positive). Under the modified condition $$xz < 0$$, the question, ‘is $$xyz > 0$$?’ is equivalent to ‘is $$y < 0$$?’, which is the same as condition 2). Since condition 1) tells us nothing about the sign of y, the answer is B. Therefore, the answer is B. Answer: B _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$79 for 1 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Re: If w^2x^3y^4z^5<0, is xyz>0?   [#permalink] 21 Jan 2018, 18:35
Display posts from previous: Sort by