How to Use the Probability Calculator
Choose from four modes: simple probability, complement, conditional probability, or expected value. Enter the required values and results appear instantly with percentage display.
Key Formulas
Simple: P(A) = favorable / total
Complement: P(A') = 1 − P(A)
Conditional: P(A|B) = P(A∩B) / P(B)
Expected value: E(X) = Σ xi × P(xi)
FAQ
What if P(B) = 0 in conditional probability?
P(A|B) is undefined when B is impossible. The calculator will show an error in this case.
Do probabilities need to sum to exactly 1?
Yes for expected value. A tolerance of 0.001 is allowed for floating-point precision. If the sum deviates more, an error is shown.