Gmat Prep?? (Arithmetic Mean)

the explanation given above by parallel_chase is fantastic.

in any case, the thing you have to look out for is this: DON'T MAKE UNWARRANTED ASSUMPTIONS.

in this problem, you must guard against the unwarranted assumption that the set of numbers is symmetrically distributed about its median / average. this assumption is reinforced by statement (1), which really does mean that the set must be symmetrically distributed, but statement (2) implies no such thing.

statement (2) talks only about the median of the set. you could have a terribly unbalanced set - say, 29, 31, 33, 35, 10982356217896452378 - with this median, and the mean would be a wildly different number.

moral of the story:
be sure to dissociate CONCEPTS from the PROBLEMS in which they appear.
for all those of you who thought the answer to this problem was (b), you probably fell prey to that trap because you are used to seeing "median" in problems that really do involve symmetrically distributed sets. if you've seen 3-4 median problems in a row in which you're told, as a precondition of the problem, that the set is symmetrically distributed (or are given a fact clearly implying that it is), it's easy to start assuming that that's always the case.
don't.