# Compound events

Sometimes, we need to deal with two or more events. These are called **compound events**. A compound event is an event that combines two or more simple events. When this happens, we need a special notation.

Given events *A* and *B*:

- The probability that
*A*and*B*occur is*P(A ∩ B) = P(A and B)* - The probability that either
*A*or*B*occurs is*P(A**∪**B) = P(A or B)*

Understanding why we use the set notation for these compound events is very important. Remember how we represented events in a universe using circles earlier? Let's say that our **universe** is 100 people who showed up for an experiment in which a new test for cancer is being developed:

In the ...

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