For question 9 I can explain the answer.
When you pick a door you have a 1/3 chance of being correct, and there is a 2/3 chance that one of the other two doors is correct. When the game show host opens one of the doors then that group of two doors still has a 2/3 chance of being correct, but now only one of those doors has that 2/3 chance of being the correct door.
