Probability Calculator. Probability for Two Event No.of Possible Outcomes- n No.of events occured- n(A) No.of events occured- n(B) Result: P(A) P(A') P(B) P(B') P(A n B) P(A U B) P(A | B) Probability for Single Event No.of Possible Outcomes- n No.of events occured- n(A) Result: Probability of Event P(A) Probability of Event not occured P(A')