Given that and are two mutually exclusive events in a
sample space , and is a probability function on
, where , , and ,
determine the value of .
The events and are complementary, so the sum of their
probabilities is equal to 1. First, use this fact to find
probability of in terms of .
The notation refers to the probability of either
event or event occurring. If and are two mutually
exclusive events, then . Now use this fact
to determine the value of .