William Sommerwerck wrote:
After you know there is a goat behind door #3 and are given
a chance to guess again, there is a 50% chance the car is
behind door #1 and a 50% chance the car if behind door #2.
Change your choice or not, you have a 50% chance of being
right.

This is not correct. I explained it in a previous post. Like this...

Because you will have initially selected the wrong door 2/3 of the
time (right?) it follows that 2/3 of the time the good prize will be
behind one of the two other doors. The host will /always/ select a
door with a goat, therefore, you should switch, because there's a 2/3
chance the other door will have the good prize.

There you go! I knew there was some good reason why my instinct told me to
switch doors, and there it is.