I don't think you understand the concept of conditional probabilities correctly.
The fact that event B already happened doesn't make it any easier to compute P(A|B) nor it renders the P(B) useless.
On the contrary P(B) and P(AB) are key to solve this problem.
I don't think you understand the concept of conditional probabilities correctly.
The fact that event B already happened doesn't make it any easier to compute P(A|B) nor it renders the P(B) useless.
On the contrary P(B) and P(AB) are key to solve this problem.