The Traditional Example of Bayesian Probability

Bayesian updating is the process of changing your beliefs based on new information. In a classic example, say you're approached by a mathematician pushing a stroller with two swaddled babies in it and can't tell what sex they are. After confirming that one of them is a girl, you knock off that boy boy option. So now the chances that they're both girls is one in three. Exactly. There's an exact amount to which you should update your belief by based off of the just the number of possibilities that there were.