Formulas
Probability of event A occurring P(A) = n(A) / n(S).
Probability of event A not occurring P(A') = 1 - P(A).
Probability of event B occurring P(B) = n(B) / n(S).
Probability of event B not occurring P(B') = 1 - P(B).
Probability of both events occurring P(A ∩ B) = P(A) x P(B).
Probability of either events occurring P(A ∪ B) = P(A) + P(B) - P(A ∩ B).
Conditional Probability P(A | B) = P(A ∩ B) / P(B).