Data Sufficiency

If xy > o, does (x-1)(y-1) = 1?

1. x+y = xy

2. x = y


They've given the answer as A. But my answer is D. Please explain me why the second equation is not sufficient

umaa wrote:If xy > o, does (x-1)(y-1) = 1?

1. x+y = xy

2. x = y


They've given the answer as A. But my answer is D. Please explain me why the second equation is not sufficient

umaa, why dont you tell us why you feel the second statement is sufficient and then I will tell you where you have gone wrong.

The simple explanation is that since x=y the equation will become (x-1)^2 and there is no way to tell whether this is equal to 1. I suspect you are using information from the first statement while solving for the second statement, which as you know is not the right way to do it.