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# If k not equal to 0,1 or -1, is 1/k >0 (1) 1/(k-1) > 0

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If k not equal to 0,1 or -1, is 1/k >0 (1) 1/(k-1) > 0 [#permalink]  25 Jan 2010, 19:46
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If k not equal to 0,1 or -1, is 1/k >0

(1) 1/(k-1) > 0
(2) 1/(k+1) > 0

How I proceeded

(1) 1/(k-1) > 0
=> k=2,3....

So 1/k>0

(2) 1/(k+1) > 0

=> k cannot be -ve ,so k is +ve and 1/k > 0

I got D.

But this is not the correct answer.Where am I going wrong
Manager
Joined: 21 Jan 2010
Posts: 50
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Kudos [?]: 15 [1] , given: 0

Re: Help needed on following math question on GMAT prep2 [#permalink]  25 Jan 2010, 20:07
1
KUDOS
gautamsubrahmanyam wrote:
If k not equal to 0,1 or -1, is 1/k >0

(1) 1/(k-1) > 0
(2) 1/(k+1) > 0

How I proceeded

(1) 1/(k-1) > 0
=> k=2,3....

So 1/k>0

(2) 1/(k+1) > 0

=> k cannot be -ve ,so k is +ve and 1/k > 0

I got D.

But this is not the correct answer.Where am I going wrong

There is no-where that states K is an integer - try to consider K as a fraction such as 1/2 or -1/2.
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Andrew
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Manager
Joined: 10 Feb 2010
Posts: 197
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Re: Help needed on following math question on GMAT prep2 [#permalink]  17 Feb 2010, 20:16
Ans: A

is 1/k > 0 => is k > 0 ?

A. 1/(k-1) >0
=> k-1>0
=> k>1
=> k>0
-- sufficient

B. 1/(k+1) > 0
=> k+1 > 0
=> k>-1 which does not mean k>0
-- insufficient
Director
Joined: 27 Jun 2008
Posts: 550
WE 1: Investment Banking - 6yrs
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Kudos [?]: 41 [0], given: 92

Re: Help needed on following math question on GMAT prep2 [#permalink]  17 Feb 2010, 22:40
gautamsubrahmanyam wrote:
If k not equal to 0,1 or -1, is 1/k >0

(1) 1/(k-1) > 0
(2) 1/(k+1) > 0

How I proceeded

(1) 1/(k-1) > 0
=> k=2,3....

So 1/k>0

(2) 1/(k+1) > 0

=> k cannot be -ve ,so k is +ve and 1/k > 0

I got D.

But this is not the correct answer.Where am I going wrong

A

(1) k has to be positive, so it's sufficient
(2) k can be -1/2, too and still meet the criteria. Insuff.
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Re: Help needed on following math question on GMAT prep2 [#permalink]  12 Mar 2010, 01:26
gautamsubrahmanyam wrote:
If k not equal to 0,1 or -1, is 1/k >0

(1) 1/(k-1) > 0
(2) 1/(k+1) > 0

How I proceeded

(1) 1/(k-1) > 0
=> k=2,3....

So 1/k>0

(2) 1/(k+1) > 0

=> k cannot be -ve ,so k is +ve and 1/k > 0

I got D.

But this is not the correct answer.Where am I going wrong

k <> 0, -1, 1
we have to prove 1/k > 0
stmt1:- 1/(k-1) > 0 to be greater than 0, k-1 has to be positive right so k-1>0 => k>1 => if k>1 defintely k>0 so 1/k>0 for sure hence this is suff
stmt2:- 1/(k+1) > 0
to be greater than 0 k+1 has to be positive, so k+1>0 => k>-1 but it does not prove if k>0 hence it is insuff.
In your approach, you are assuming that k is always integer. but k can be fraction also.
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Re: Help needed on following math question on GMAT prep2   [#permalink] 12 Mar 2010, 01:26
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