Calculate the probability of one event, its complement, and simple independent AND/OR combinations.
Averages, standard deviation, z-scores, normal distributions and probability calculations.
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If A has probability 0.5 and B has probability 0.25, independent P(A and B) is 0.125.
Calculate the probability of one event, its complement, and simple independent AND/OR combinations. The result is intended for quick estimates, checking arithmetic and comparing scenarios. When a result affects a contract, tax filing, medical decision, building-code requirement or other high-stakes situation, verify the result with the appropriate professional or authoritative source.
If event A has probability 0.40 and independent event B has probability 0.25, then P(A and B) = 0.40 × 0.25 = 0.10. The probability that at least one occurs is 0.40 + 0.25 − 0.10 = 0.55.
Critical assumption: these “and” and “or” formulas assume independence. If events affect each other, you need conditional or joint probabilities instead; entering marginal probabilities alone cannot give a reliable combined result.
Calculate the probability of one event, its complement, and simple independent AND/OR combinations.
For independent events, P(A and B) = P(A)×P(B). P(A or B) = P(A)+P(B)−P(A)P(B).
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