Please correct me on this:
Check on host's logic, when he has to choose between 2 doors and when he doesn't has to.
Car is behind A.
P(win) = P(1/3 Ben chooses A, 1/2 host shows C, 1/2 Ben stays) + P( 1/3 Ben chooses A, 1/2 host shows B, 1/2 Ben stays) + P(1/3 Ben chooses B, 1/1 host shows...