Data Sufficiency

Hi everyone,

Here is an example I stumbled across quite recently:

If X^3*Y = 24, what is the value of (X^3*Y^3 - X^2*Y^2)?
(1) X^2*Y^2 = 36.
(2) X^3*Y^2 = 72.

The answer page says the correct one is B. However, the statement(1) is also sufficient, since:

X^2*Y^2 = 36 => X*Y = +-6, but if X^3*Y is positive, X*Y can only be positive.
Therefore, X^2*Y^2(X*Y-1)=36(X*Y-1)=36*5 = 180

Please correct me if I'm wrong.

yes you are correct, statement 1 is also alone sufficient.

I think they forget to frame the part of solution that you have discovered.

There are a lot of questionable question sources out "there".

Hence, it's always good to post the source of questions. If you told me your question was from Kaplan or MGMAT, I'd be surprised. If you told me it was from some semi-random question set you downloaded for free of the Net, I wouldn't be shocked at all.