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Is x > 0? (1) -2x > 0 (2) x^3 < 0

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GMAT 1: 620 Q46 V29
Is x > 0? (1) -2x > 0 (2) x^3 < 0 [#permalink]

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New post Updated on: 21 Mar 2017, 12:31
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Is x > 0?

(1) -2x > 0

(2) x^3 < 0

Originally posted by vmelgargalan on 21 Mar 2017, 12:29.
Last edited by vmelgargalan on 21 Mar 2017, 12:31, edited 1 time in total.
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Re: Is x > 0? (1) -2x > 0 (2) x^3 < 0 [#permalink]

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New post 21 Mar 2017, 12:31
I am confused as to why the answer is D. Because for option 2 x could be positive or negative. So we can't be sure whether x is larger or smaller than 0
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Re: Is x > 0? (1) -2x > 0 (2) x^3 < 0 [#permalink]

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New post 21 Mar 2017, 12:42
vmelgargalan wrote:
Is x > 0?

(1) -2x > 0

(2) x^3 < 0

I am confused as to why the answer is D. Because for option 2 x could be positive or negative. So we can't be sure whether x is larger or smaller than 0


How does positive value satisfy x^3 < 0? (positive)^3 > 0 and (negative)^3 < 0.
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Re: Is x > 0? (1) -2x > 0 (2) x^3 < 0 [#permalink]

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New post 21 Mar 2017, 12:54
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vmelgargalan wrote:
Is x > 0?

(1) -2x > 0

(2) x³ < 0


Target question: Is x > 0?

Statement 1: -2x > 0
Divide both sides by -2 to get: x < 0 (we reverse the inequality symbol because we divided by a NEGATIVE value)
If x < 0, then the answer to our target question is NO, it is not the case that x > 0
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: x³< 0
There are a few ways to handle this. Here's one approach.
Since x³< 0, we can be certain that x ≠ 0, which also means that x² is POSITIVE
If x² is POSITIVE, we can take x³< 0 and divide both sides by x² to get: x < 0
If x < 0, then the answer to our target question is NO, it is not the case that x > 0
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer:

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Joined: 16 Jan 2017
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Re: Is x > 0? (1) -2x > 0 (2) x^3 < 0 [#permalink]

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New post 21 Mar 2017, 16:42
Bunuel wrote:
vmelgargalan wrote:
Is x > 0?

(1) -2x > 0

(2) x^3 < 0

I am confused as to why the answer is D. Because for option 2 x could be positive or negative. So we can't be sure whether x is larger or smaller than 0


How does positive value satisfy x^3 < 0? (positive)^3 > 0 and (negative)^3 < 0.


Yep, you are right. Had a brain fart. It doesn't. Silly, that this was the only wrong question I got... Once again I read the question too fast and I thought both signs were in the same direction.
Re: Is x > 0? (1) -2x > 0 (2) x^3 < 0   [#permalink] 21 Mar 2017, 16:42
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