Conditional Probability

If A and B are two events of the same sample, S, then:

The conditional probability of event A on B, P (A|B), is the probability of event A when the event of B has already occurred.

Conditional Probability Formula


Calculate the probability of a 6 being rolled by a die if it is already known that the result is even.

Conditional Probability Example

Independent Events

Two events A and B are independent if:

p(A|B) = p(A)

Dependent Events

Two events A and B are dependent if:

p(A|B) ≠ p(A)