re: probability 4 geffa Well geffa maybe I am wrong for once. Search google for "monty hall problem". It seems that IF 'U Assume that the host always chooses to open a door with a Booby Prize, and would never reveal the Grand Prize'
then U should always switch.
see http://people.hofstra.edu/staff/steven_r_costenoble/MontyHall/MontyHall.html
But if host opens door at random so sometimes host opens door with $100 then 50/50.
Live and learn.
