Data Sufficiency

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

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

I keep getting A,
OA is D.

Moved the DS question to the DS forum...

1 - sufficient. 1/(k-1) > 0 implies k-1 is positive. i.e. k-1 > 0 or k > 1
So, 1/k > 0

2 - 1/(k+1) > 0 implies k+1 > 0 or k > -1.
If k is an integer, we know k cannot be 0 or 1 and so 1/k > 0

Does the question state that k is an integer. If it doesn't, I think (2) is not
sufficient - take k=-0.5 for example 1/(k+1) > 0 but 1/k < 0.

nope, it didn't state it I don't think. When I copied them I was going back and forth switchiing screens making sure I wrote them down correctly on the post.

I looked at the whole fraction as opposed to k + 1 >0...thinking mathematically for this test helps I guess...

My explaination is:

(1) -1/(k-1) > 0 . If you times (-1), you will get 1 / (k-1) < 0 . Because k can't be 0, K has to be negative in order to make 1/ (k -1) < 0.

(2) -1/ (k +1) > 0. If you times (-1), you will also get 1/ (k+1) < 0. K has to be negative to make the equation is valid.

The answer is D.

highfive287 wrote:My explaination is:

(1) -1/(k-1) > 0 . If you times (-1), you will get 1 / (k-1) < 0 . Because k can't be 0, K has to be negative in order to make 1/ (k -1) < 0.

(2) -1/ (k +1) > 0. If you times (-1), you will also get 1/ (k+1) < 0. K has to be negative to make the equation is valid.

The answer is D.

highfive287, you misunderstood a hyphen after the equation number to mean a negative sign. Viz. 1- and 2- ...

So, its not -1/(k-1), its 1/(k-1)
Also, its not -1/(k+1), its 1/(k+1)

Here is my thinking:

for 1/k to be greater than 0, i.e. for 1/k > 0 to be true, k must satisfy this range:

0 < k <= 1 .......... (eq1)

That means, that k should be a fraction, less than 1 but still positive.

(1) 1/(k-1) > 0
For this to be true, applying the same logic as above
= 0 < (k-1) <= 1 must be true
= 1 < k <= 2 must be true
this violates the above (eq1) with certainty and hence is SUFFICIENT to answer the original question. The answer would be NO, 1/k is not greater than 0, but we are not interested in the answer.

(2) 1/(k+1) > 0
For this to be true, applying the same logic as above
= 0 < (k+1) <= 1 must be true
= -1 < k <= 0 must be true
this violates the above (eq1) with certainty and hence is SUFFICIENT to answer the original question. The answer would be NO, 1/k is not greater than 0, but we are not interested in the answer.

Final answer would be (D), each statement alone is sufficient.