I understand and agree with the Marilyn Savant solution, but I have a different intuition which I have not tested. Once one of the doors has been eliminated, my intuition would be to flip a coin to choose whether to stay or switch. I would have to play with this to see if it is an equivalent solution, but I thought I would put it out there for others to play with. It has the intuitive advantage of symmetry that seems appropriate for choosing one of two closed doors.