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# Is x/y^3>0?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 7599
GMAT 1: 760 Q51 V42
GPA: 3.82

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06 Mar 2018, 03:57
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Difficulty:

15% (low)

Question Stats:

78% (00:50) correct 22% (01:19) wrong based on 58 sessions

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[GMAT math practice question]

Is $$\frac{x}{y^3}>0$$?

1) $$x-y>0$$
2) $$xy>0$$

_________________
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" VP Joined: 31 Oct 2013 Posts: 1392 Concentration: Accounting, Finance GPA: 3.68 WE: Analyst (Accounting) Re: Is x/y^3>0? [#permalink] ### Show Tags 06 Mar 2018, 04:37 MathRevolution wrote: [GMAT math practice question] Is $$\frac{x}{y^3}>0$$? 1) $$x-y>0$$ 2) $$xy>0$$ we are looking for whether x/y^3 >0 or not in order to answer this question we have do know that quotient will be positive if both numerator and denominator are positive or both negetive. 1) x-y > 0 from this statement , we only know x> y but we know anything about their signs. clearly insufficient. 2) xy> 0 it means that either x and y both are positive or both negative. thus , it's sufficient. Answer is B. VP Status: Learning Joined: 20 Dec 2015 Posts: 1033 Location: India Concentration: Operations, Marketing GMAT 1: 670 Q48 V36 GRE 1: Q157 V157 GPA: 3.4 WE: Engineering (Manufacturing) Re: Is x/y^3>0? [#permalink] ### Show Tags 06 Mar 2018, 09:48 MathRevolution wrote: [GMAT math practice question] Is $$\frac{x}{y^3}>0$$? 1) $$x-y>0$$ 2) $$xy>0$$ Good question x/y^3 >0 so the question basically ask whether x and y have same sign as x/y^>0 if they have same sign . From 1 x=3 y=2 then 3/8 >0 but when x=3 and y=-2 3/-8^3 <0 so insufficient From 2 They have same sign therefore x/y^>0 hence sufficient . The answer is B _________________ Please give kudos if you find my answers useful Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7599 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: Is x/y^3>0? [#permalink] ### Show Tags 08 Mar 2018, 02:22 => 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. We then recheck the question. The question can be modified as follows: $$\frac{x}{y^3}>0 ⇔ xy>0.$$ This can be seen by multiplying both sides by $$y^4$$. It is same as condition 2). Condition 1) If $$x = 2$$ and $$y = 1, xy = 2 > 0$$, and the answer is ‘yes’. If $$x = 2$$ and $$y = -1, xy = -2 < 0$$, and the answer is ‘no’. Since we don’t have a unique answer, condition 1) is not sufficient. Therefore, the answer is B. Answer: B If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59% chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but there may be cases where the answer is A,B,C or E. _________________ 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"
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Re: Is x/y^3>0?   [#permalink] 08 Mar 2018, 02:22
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