00:01
We'll do both parts with the same tool, conditional probability.
00:04
The key is what does monty's action tell you? so for a, you pick a door, say a, and monty randomly tries to open one of the other two doors and happens to reveal a goat.
00:16
Now switch or stay.
00:17
Let c sub a be equal to the car behind your chosen door a.
00:21
So the prior would be p of c sub a is equal to one third.
00:26
If the car is behind a, monty will always be able to open a goat.
00:30
Both other doors are goats.
00:32
So the probability that a goat is opened given c -s -s -a is going to be equal to one.
00:41
If the car is not behind a, which is probability of two out of three, then on the two other doors, one is a car, one is a goat.
00:49
So monty randomly picks one to open.
00:52
So the probability that it's a goat opened, given the complement of c -s -s -a, would be one -half...