Addition Rule (Union of Events)
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Tap a term to see what it means, or .
Calculate
Example: in a class, 60% of the students like maths, 45% like physics and 30% like both. Picking a student at random, what is the chance they like at least one? Change the values to work out your own case.
Step by step
What each term means
- Union (P(A ∪ B))
- The chance that A happens, or B, or both: at least one of them.
- Probability of A
- Includes the cases where only A happens and those where A and B happen together.
- Probability of B
- Also includes the intersection. Adding P(A) and P(B) counts the cases of both twice.
- Intersection (P(A ∩ B))
- The chance of both happening together. Subtracting it once undoes the double count. If A and B can't happen together, it is zero and the union is a plain sum.