Joint Probability of Two Events
The probability of two events A and B happening concurrently is called the "joint probability" of the two events.
Simplest Case
If the events are mutually exclusive (or disjoint),
the joint probability of A and B is 0, or P(A and B) = 0.
General Case
If the events are not mutually exclusive,
the joint probability of A and B may be found using either the Addition Rule or the Multiplication Rule of Probability, depending on the information given in the problem.
The Multiplication Rule may be used if the probability of one of the events is known and the conditional probability of the other in relation to the first is also known. Then the joint probability of A and B may be found using one of the following formulae.
The Addition Rule may be used if the probabilities of both individual events are known and the probability of A or B happening is also known. Then the joint probability of A and B may be found using the following derivative of the Addition Rule.
Last Updated by SAS October 07, 2026, 16:00:54
