Probability Calculator
Calculate probability of events, compound probability, combinations, and permutations
Event Inputs
P(E) = favorable / total
Results
Enter favorable and total outcomes
Frequently asked questions
What is the probability formula?
The basic probability formula is P(E) = (number of favorable outcomes) ÷ (total number of possible outcomes). For example, rolling a 3 on a fair die has probability 1/6 ≈ 16.67%.
What is the difference between combinations and permutations?
Combinations C(n,r) count the number of ways to choose r items from n when order does not matter. Permutations P(n,r) count ordered arrangements. C(n,r) = n! / (r!(n−r)!), P(n,r) = n! / (n−r)!.
What does independent vs mutually exclusive mean?
Independent events do not affect each other — P(A∩B) = P(A)×P(B). Mutually exclusive events cannot both occur at the same time — P(A∩B) = 0 and P(A∪B) = P(A) + P(B).
What is complementary probability?
The complement of event E is the probability that E does NOT occur. P(not E) = 1 − P(E). For example, if P(rain) = 30%, then P(no rain) = 70%.