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OR Probability Calculator

Find the probability that at least one of two events occurs.

P(A or B) 0.65

Formula: P(A or B) = P(A) + P(B) − P(A and B)

Step-by-step with your numbers:
1. Values used:
2. P(A) = 0.5
3. P(B) = 0.3
4. P(A and B) = 0.15
5.
6. P(A or B) = 0.65
Did we solve your problem today?

The chance of either event uses inclusion–exclusion to avoid double-counting the overlap.

The math behind it

P(A or B) = P(A) + P(B) − P(A and B). For mutually exclusive events the overlap is 0.

Worked example

0.5 + 0.3 − 0.15 = 0.65.

FAQ

Mutually exclusive events?

Set P(A and B) = 0; then just add the probabilities.

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