Probability Calculator
Combine event probabilities. Assumes independence unless noted.
Probabilities
Result
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Formulas
- P(A and B) = P(A) · P(B) — for independent events.
- P(A or B) = P(A) + P(B) − P(A and B).
- P(not A) = 1 − P(A).
- P(at least once in n) = 1 − (1 − p)ⁿ.
- Binomial: P(X = k) = C(n, k) · pᵏ · (1−p)ⁿ⁻ᵏ.
Independence assumption
"Independent" means the outcome of A doesn't change the probability of B. Coin flips are independent. Drawing cards without replacement is not. If your events influence each other, use conditional probability formulas instead.