回複：Monty Hall Problem

he should switch,
he double the change by switching
the probability to get a car changes from 1/3 to 2/3
you can get it by calculate the conditional probability,

here there is another way to get it,
1. it is not hard to see that, the first door he chooses has a probability 1/3 to be the $$ door
2. therefore in a little rounded way, the only door left has a probability 2/3 to be the $$ door, since the probability sums up to 1.