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# DS - Inequality

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Manager
Joined: 08 Feb 2009
Posts: 144
Schools: Anderson

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03 May 2009, 15:16
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GMAT Tutor
Joined: 24 Jun 2008
Posts: 1346

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03 May 2009, 15:52
S2 is clearly insufficient alone.

S1 will always be true if x is negative and y is positive, in which case xy < 0. S1 can also be true when both x and y are positive, or when both are negative (e.g. take x = 2 and y = 1), in which case xy > 0. So S1 is insufficient.

Taken together, if x > 0, then 1/x > 0. Since 1/y > 1/x > 0, y must also be positive, and xy must be positive. So we can answer the question, and the answer is 'no'. C.
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Manager
Joined: 08 Feb 2009
Posts: 144
Schools: Anderson

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03 May 2009, 16:08
IanStewart wrote:
goldeneagle94 wrote:
Need help for this as well.

Is ab < 0 ???

1) (a/b) > 1

2) a > 0

thanks.

S2 is clearly insufficient alone. From S1, we know that a/b is positive. If a/b is positive, then a and b must have the same sign - both positive or both negative. Either way, ab is also positive, so we can answer the question: the answer is 'no'. A.

The question is similar to the one in Quotes.

Statement 1 can also be simplified like this
(1/x) < (1/y)
1 < (x/y) (multiplying both sides by x)
(x/y) > 1

If the above is correct, then it is the same question as in Quotes.
Then, How can we have Two different answers ???
I have tried and could not get over this.
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1346

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03 May 2009, 17:28
1
KUDOS
Expert's post
goldeneagle94 wrote:
The question is similar to the one in Quotes.

Statement 1 can also be simplified like this
(1/x) < (1/y)
1 < (x/y) (multiplying both sides by x)
(x/y) > 1

If the above is correct, then it is the same question as in Quotes.
Then, How can we have Two different answers ???
I have tried and could not get over this.

You can't multiply both sides by x here; you don't know if x is positive or negative. If x is negative, you'd need to reverse the inequality after multiplying on both sides by x. Once you know (from Statement 2) that x is positive, then you can multiply on both sides, and it becomes like the other question you posted.
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Re: DS - Inequality   [#permalink] 03 May 2009, 17:28
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