Union and Intersection in Probability
When A and B are events, read intersection and union as follows.
| symbol | meaning | read as |
| ∪ | union | or |
| ∩ | intersection | and |
| ' | complement | not |
Some examples:
- A ∩B : A and B happen
- A ∪B' : A or not B happen, i.e. A happens or B doesn't
To visualise examples of not, the table view is often easier to use. Have a look at these diagrams.
To visualise set complements and unions, it can sometimes help to transform it as follows. Replace each set by its complement (remembering (A')' = A) and replace ∪ by ∩, then complement the whole thing.
For example, A∪B' = (A'∩B)' - in other words, everything that isn't both B and not-A.