Final answer:
Disjoint events, or mutually exclusive events, are two outcomes that cannot occur at the same time, which means the probability of e and f happening together is zero.
Step-by-step explanation:
If e and f are disjoint events, then the probability of both events occurring at the same time is zero (P(e AND f) = 0). In probability theory, two events are considered to be mutually exclusive if they cannot happen simultaneously. This concept is crucial in determining the probabilities of different outcomes and is a foundational principle in statistics.
For example, consider two events A occurring and B not occurring in a single toss of a fair coin. Here, event A is getting a tail, and event B is getting a head. Since a coin toss can only result in either heads or tails, not both, A and B are mutually exclusive. Applying this to general events e and f, the fact that they are disjoint means that if event e occurs, event f cannot occur, and vice versa.