Is X a multiple and factor of itself

If X is a positive integer, then yes. As an example, if X = 12, the multiples of X are ...-24, -12, 0, 12, 24, ... and the positive divisors of X are 1, 2, 3, 4, 6, and 12.

wilderness wrote: 1) do we really talk about factors of a -ve number ?

2) If yes, then why does this rule not apply to that case. Afterall just like 2/2 = 1 and -2/-2 = 1 and 2*1=2 and -2*1 = 2.

Thanks in advance.

Re 1), not in any GMAT question I've ever seen. I've only ever seen GMAT questions that ask about 'positive divisors', and divisibility questions seem to always be restricted to positive integers.

The rules are, as you point out, the same for negatives and positives- when I was restricting things to positives in my first post, I was actually only trying to exclude zero (zero is a bit of an exception- zero is a multiple of itself, but not a divisor of itself- that's not a technicality you need to be concerned about for the GMAT). And, of course, I was limiting the discussion to the case that's relevant on the GMAT.