Final answer:
The sum rule of probability is applied when determining the probability of either one event or another occurring, with the key indicators being the words 'either' and 'or'. This rule is relevant when dealing with mutually exclusive events and the calculation involves adding their individual probabilities.
Step-by-step explanation:
The key indicators for applying the sum rule of probability are the words either and or. The sum rule is used to calculate the probability of one event or another event occurring when the two events are mutually exclusive. This means that the events cannot happen at the same time. For example, when flipping two coins, and you want to know the probability of getting a head on one coin or a tail on the other, you would apply the sum rule and add the individual probabilities of each event occurring separately.
To clarify further, mutually exclusive events are such that the occurrence of one event excludes the possibility of the other event occurring. Therefore, in practice, you calculate the probability of each event individually and then sum these probabilities together. The formula for the sum rule is P(A OR B) = P(A) + P(B), assuming that A and B are mutually exclusive events. In cases where they are not mutually exclusive, you must also subtract the probability of both events occurring together: P(A OR B) = P(A) + P(B) − P(A AND B).