Thanks Stuart.
Stuart Kovinsky wrote:
Let's simplify the question:
is XY divisible by 9?
(1) x = 9
this might seem sufficient at first glance, but what if y = 1/2? In that case, then xy = 4.5, which is certainly not a multiple of 9.
They key to this question is to realize that Y doesn't have to be an integer; for all integer values of Y we get a "yes" answer (from (1) or (2) alone), but for most non-integer values of Y we get a "no" answer, even after combining the statements.
