Originally Posted by
pinniped
Yes - it makes perfect sense. The thing a lot of people leave out when they get confused on the Monty question is the fact that Monty knows where the prize is. He uses this knowledge to always open a nonwinning door.
It is because of this rule - the fact that Monty applies knowledge to avoid opening the winning door - that switching your guess yields a 2 in 3 chance of winning.
Right. He adds information about the third door by opening the second door, but doesn't add any information about the first door.