I give you a choice of one of three large boxes. One box contains a new car and the other two boxes each contain an old goat. You choose one box. Then I show you the contents of one of the remaining boxes, and it proves to be a goat.
I now offer you the opportunity of changing your mind and selecting the remaining unopened box. Should you remain with your original choice or should you change your mind and select the remaining unopened box?
to view a BASIC program giving you the answer and running a test to prove it. Don't worry if you are not running BASIC, as the program is in ASCII and you can read the answer and follow the logic by reading the text. If you do have BASIC then save the file and run it later.