If and are two events in a sample space of a random experiment, where , , and , determine .
The events and are complementary, so the sum of
their probabilities is equal to 1. First, use this fact to find
the probability of
The notation refers to the probability
of either event or event occurring, or both. Since and
are two non-mutually exclusive events, then where the notation refers to the probability of events
and occurring together. Now use this fact, along with the fact
that to find the probability of
Thus, the probability of is equal to 0.75.