Conditional probability measures the likelihood of an event occurring given that another event has already occurred. It's denoted as P(A|B), which reads as "the probability of A given B."

Conditional probability allows us to update our beliefs based on new information, making it a fundamental concept in statistical reasoning and decision-making.

Definition

For two events A and B where P(B) > 0, the conditional probability of A given B is defined as:

This formula can be interpreted as the proportion of outcomes in B that also belong to A.