Answer
If it is impossible for events $ A\ \text{ and }\ B $ to occur simultaneously, the events are said to be mutually exclusive. For such events $ P\left( A\ \text{or}\ B \right)=P\left( A \right)+P\left( B \right)$.
Work Step by Step
We know that if it is impossible for any two events, $ A\ \text{ and }\ B $ to occur simultaneously, they are said to be mutually exclusive.
If $ A\ \text{ and }\ B $ are mutually exclusive events, the probability that either $ A\ \text{or }B $ will occur is determined by adding their individual probabilities.
Thus, the probability is:
$ P\left( A\ \text{or}\ B \right)=P\left( A \right)+P\left( B \right)$
