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DS - positive or negative [#permalink]
21 Nov 2007, 06:59

If K is not equal to 0, 1, -1, is 1/k >0?

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

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

I chose D, but the OA is A.
In statement 1, the only way it can be positive is to have K greater than or equal to 2, which subsequently 1/k will always be positive.
As for statement 2, the only way it can be positive is also by using a number either greater than or equal to 2 in order to end up with 1/k as positive, yet according to the OA, statement 2 is not suff. can someone explain to me how?
thanks

Re: DS - positive or negative [#permalink]
21 Nov 2007, 07:03

tarek99 wrote:

If K is not equal to 0, 1, -1, is 1/k >0?

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

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

I chose D, but the OA is A. In statement 1, the only way it can be positive is to have K greater than or equal to 2, which subsequently 1/k will always be positive. As for statement 2, the only way it can be positive is also by using a number either greater than or equal to 2 in order to end up with 1/k as positive, yet according to the OA, statement 2 is not suff. can someone explain to me how? thanks

I got A.

Statement 2 works if say, x = -0.9 as it would read - 1/0.1 >0
However, 1/-0.9 < 0

A, as statement b fails when k=-0.5 or any other decimal lower than 1.

Did you plug in the different values of "K" or did you solve the inequality in general? Could you please elaborate on logical approach?

LM wrote:

If K is not equal to 0,1,-1, is 1/k > 0?

( i ) 1/(k-1)>0

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

A My reasoning: the question is similar to k>0?, and keep the condition of k in mind. Go 1, 1/(k-1) >0, again similar to k-1 >0, so k>1, not only satify the conditions but also answer the question. Sufficient 2. again: k+1>0, so k>-1. Stop and think a little. Although combined with the conditions " k is not equal 0, 1, even -1, it still not enought to answer the question. k still can be equal to any fraction running from -1 to 0. Right? _________________