If all variables are positive, is (w/x) > (y/z)?

1) w = y + 50
2) x = z + 50

1) and 2) alone are INS.

(y+50)/(z+50) > y/z
yz +50z > yz +50y
50y > 50z
y > z

Both together are INSUFICIENT so E)

My question is, however: The first time that I worked it out, I simply did this...

If w = y + 50 , then w > y
If x = z + 50 , then x > z

Divide equations by each other:

(w > y) ÷ (x > z) = (w/x) > (x/z)

Why isn't this right?