Data Sufficiency

kwah wrote:Attached is a word problem from GMATPrep Test.

Answer: C

Can someone please explain the steps to achieve this result?

Thank you,
K

Is mx + ky > kx + my?
OR mx - my + ky - kx > 0
OR m(x - y) - k(x - y) > 0
OR (m - k)(x - y) > 0
This means that for the above inequality to be true, both m - k and x - y should be positive or both of then should be negative.

Statement (1): m > k or m - k > 0, but we have no info about x - y; NOT sufficient.
Statement (2): x > y or x - y > 0, but we have no info about m - k; NOT sufficient.

Combining (1) and (2): We know that both m - k and x - y are positive. So, (m - k)(x - y) > 0; SUFFICIENT.

The correct answer is C.