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-2x > 3y, is x negative?

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-2x > 3y, is x negative?

by vzzai » Fri Nov 25, 2011 5:42 pm
If -2x > 3y, is x negative?

(1) y > 0

(2) 2x + 5y - 20 = 0

[spoiler]1) x>-3/2 (x could take negative, 0 or positive)- Not-sufficient
2) 2x+5y=20 (x could take negative, 0 or positive) - not sufficient
1)& 2) not sufficient - I went for E. [/spoiler]

One of the answers from a site says D as answer. Please explain.

Source:GMATPrep
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Source: — Data Sufficiency |
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by HSPA » Fri Nov 25, 2011 6:06 pm
A) is good

as we know Y is positive, -2x shall be positive.. this happens only when X is negitive.

B) sounds not so good

-2x = 5y-20
we know -2x > 3y , let us consider two values for -2x => 4y and 8y
for -2x = 4y we get y as positive (after substitution)
for -2x = 8y we get y as negitive

To me only A is the answer.
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by pemdas » Fri Nov 25, 2011 6:41 pm
If -2x > 3y, is x negative?

(1) y > 0

(2) 2x + 5y - 20 = 0
st(1) says y>0 hence 3y>0 and -2x>0, we may conclude x is negative as -ve*-ve=+ve (here required), ans. Yes, Sufficient
st(2) 2x+5y=20 with the question stem -2x>3y (or 2x<-3y); 2x=20-5y<-3y, 20<2y, y>10, hence y is +ve.
from the question stem -2x>3y and x<-3y/2, because y is +ve, here x must be -ve, ans. Yes, Sufficient

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by tpr-becky » Fri Nov 25, 2011 6:51 pm
This is a great question for positive negative.

From the stem we know that if y is positive then x is negative and if y is negative then x is positive thus we will be generally looking for whether y is positive or negative.

1) tells us that y is positive thus x must be negative - sufficient, AD

2) This looks trickier - but remember to look for curve balls - we know that 2x = 20 -5y so it seems that x and y could be positive or negative - however you have to remember that the soution must also fit the statement that -2x >3y which means that 2x <-3y (you flip the sign when dividing or multiplying by a negative). now you have two pieces of info that will relate to each other and you can set them equal if 2x = 20 - 5y then we know that 20- 5y <-3y. Now manipulate by adding 5y to each side to get 20 <2y whis menas that 10<y which means y is positive. Thus this is sufficient as well and the answer is D.
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by HSPA » Fri Nov 25, 2011 6:53 pm
silly mistake :) .. D is good
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by vzzai » Fri Nov 25, 2011 6:58 pm
Thanks all. I know my mistake. Exam stress is causing silly mistakes...:(
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by pemdas » Fri Nov 25, 2011 7:09 pm
no stress or time constraint may abort thinking process when it's well-established
so wide are concepts of +ve/-ve, the PhD topics are elaborated on them
@vzzai, get back to this q. and analyze it thoroughly instead of remembering your stressful mood from sitting in PVue examination room
vzzai wrote:Thanks all. I know my mistake. Exam stress is causing silly mistakes...:(
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