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this problem comes from noel's site - http://www.geocities.com/gmatcrew/noel.htm
(hope, everybody knows that person from bweek-forums).
if x and y are prime, is xy odd?
1. x-y is even
2. x/y is not an integer
i voted for A. obviously, only subtracting prime from prime gives us even (you don't count 2, since it will contradict with statement 1). thus, 1 is suff. statement 2 is not suff., because we don't know either it 2/3 or 3/5 or whatever. since prime 2 is a key here and we are not sure whether it exists or not, statement 2 is not suff. but noel says, i am wrong
ps. unfortunatelly, it is diagnostic test and noel does not give any right answer. he just agrees with you, if you are right ('ok') or puts question mark '?' if you are wrong...