Data Sufficiency

Hi,
Could someone please help me understand the answers to the following three GMATPrep problems? Thanks.

1) If k is not equal to 0,1 or -1, is 1/k > 0?
i) 1/ (k-1) > 0 (Sufficient)
ii) 1/ (k+1) > 0 (Don't know)


2) When the +ve integer n is divided by 25, the remainder is 13. What is the value of n?
i) n< 100 (obviously, insufficient)
ii) When n is divided by 20, the remainder is 3.


3)If the numbers X and Y are not integers, the value of X is closest to which integer?
i) 4 is the integer that is closest to X + Y
ii) 1 is the integer that is closest to X -Y



Thanks.
Shilo