Probability of Two Events Calculator
Combines two probabilities, once you know how the events relate.
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The formula
independent: P(A and B) = P(A) × P(B) exclusive: P(A and B) = 0 P(A or B) = P(A) + P(B) − P(A and B)
Independent means one event happening does not change the chance of the other. Mutually exclusive events are not independent: one happening rules the other out.
What to watch out for
Multiplying probabilities assumes independence, which is a common and sometimes costly mistake. Check whether one event makes the other more likely.
Frequently Asked Questions
What is a worked example?
With independent chances of 30% and 50%, both is 15%, either is 65% and neither is 35%.
What is the difference between independent and mutually exclusive?
Independent events do not affect each other. Mutually exclusive events cannot happen together, which is a strong effect on each other.