Calculate basic, complement, union, intersection, conditional, and Bayes' theorem probabilities — with Venn diagram logic and step-by-step working for each type.
Probability Type
Probability
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Probability
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As Fraction
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Percentage
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Odds
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Select a probability type above
All probabilities must be between 0 and 1 (inclusive).
Frequently Asked Questions
What is a complement probability?
The complement of event A is everything that is NOT A. P(A') = 1 − P(A). For example, if P(rain) = 0.3, then P(no rain) = 0.7.
What is Bayes' Theorem?
Bayes' Theorem: P(A|B) = P(B|A) × P(A) / P(B). It updates the probability of hypothesis A given new evidence B. Used widely in medical testing, spam filtering, and machine learning.