anantbhatia wrote:If x and y are distinct positive integers, what is the value of x^4 - y^4?

(y2 + x2)(y + x)(x - y) = 240
xy = yx and x > y

[spoiler]Source: Platinum GMAT OA:D[/spoiler]

Not satisfied with the explanation posted there. I doubt if it is a good level qn.

Statement 1 is sufficient; if you expand the left side, you get x^4 - y^4.

Statement 2 is clearly not sufficient. Of course xy = yx; that's always true, so that isn't useful information. We already know that x and y aren't equal, so x > y only tells us that x^4 - y^4 is positive. It might be that y = 1 and x = 2, or that y = 1 and x = 3, and the value of x^4 - y^4 will be different in each case. So the answer is A unless Statement 2 has been miscopied.