"Bernie Cosell" <bernie@fantasyfarm.com> wrote:

Right, and just to summarize here: it seems to be identical with the Monty Hall problem, EXCEPT: that the instructor informed the students of a wrong-choice on the exam *without* knowing which choice the student had made. The question addressed is whether the instructor's 'revelation' being random, rather than knowingly NOT selecting the one the player/student chose, affects the odds.

Just to be complete, I should say that the instructor informed the students that choice C was wrong. The question was asked from the standpoint of a student who initially answered A. Of course, the students who chose C should change their answer, just as when Monty Hall shows you a goat behind the door you picked, and asks you if you want to switch. In case that's too hard to figure, he could show you the car behind a door you didn't pick and ask you if you want to switch. Of course, MvS is still is ignoring the case where the host doesn't always give the contestant a chance to switch. Dan