1. The problem statement, all variables and given/known data Three concentric hollow spherical conductors are charged as follows: the inner conductor carries charge Q, the middle conductor carries charge -2Q, and the outer conductor carries charge -Q. What is the charge on the outer surface of the middle conductor? 2. Relevant equations Flux= Qenc / ε0 3. The attempt at a solution Because the flux inside a conductor has to be zero, I drew a gaussian surface in the second conductor, since the first conductor is carrying Q, the inner surface of the 2nd conductor should carry -Q, and the outer surface, to neutralize that should carry Q. This is incorrect, and the correct answer is apparently -Q.