Official Solution:
If you take the 1st step of the variable approach and modify the original condition and the question, you can see that it is a "2 by 2 question" which frequently appears in the current Gmat math as shown in the table below.
finance marketing Number f m Average salary x y
Question: \(\frac{fx+my}{f+m} > \frac{x+y}{2}\) ? and if you expand this, you get \(2(fx+my)>(f+m)(x+y)\)?, or \(2fx + 2my>fx + fy + mx + my\)?. If you move this to one side, you get \(fx + my - fy - mx > 0\)?, \(f(x-y) - m(x-y)>0\)?, or \((f-m)(x-y)>0\)?.
In the original condition, there are 4 variables \((f,m,x,y)\). In order to match the number of variables to the number of equations, there must be 4 equations. Therefore, E is most likely to be the answer.By solving con 1) & con 2), you get from \(f < m\) (by con 2) and \(x = y - 10,000\) to \(f - m < 0\) and \(x - y = -10,000 < 0\), then finally to \((f- m)(x - y) = ( - )( - ) > 0\), hence always yes and sufficient.Therefore, the answer is C.
Answer: C