Final answer:
The probability P(E U E') represents the likelihood that either event E, event E', or both events happen. For mutually exclusive events, this probability is the sum of their individual probabilities, whereas for non-mutually exclusive events, the probability of both occurring together is subtracted from the sum of their individual probabilities.
Step-by-step explanation:
The probability P(E U E') represents the chance that one of the events occurs, or both occur. To elaborate, if we're considering two events E and E', the union of these events (E U E'), also expressed as P(E OR E'), encapsulates all the outcomes where either event E happens, event E' happens, or both events occur simultaneously. In terms of probability calculation, for mutually exclusive events, this probability would be the sum of their individual probabilities since they cannot both occur at the ame time. However, if the events are not mutually exclusive, we must then subtract the probability of both E and E' occurring together (P(E AND E')), as it is counted twice when we add P(E) and P(E').
For non-mutually exclusive events, the probability that at least one of them occurs is represented by the formula P(E OR E') = P(E) + P(E') - P(E AND E'), while for mutually exclusive events, it simplifies to P(E OR E') = P(E) + P(E') because P(E AND E') would be zero in this case.