Final answer:
The statement is partially true; the sum rule applies to adding probabilities of mutually exclusive events. For independent events occurring together, the product rule, which involves multiplying probabilities, is used instead.
Step-by-step explanation:
The statement "To find the probability of an event, add up the probabilities of the outcomes that make up the event" is partially true. This description applies to certain situations governed by the sum rule of probability, specifically when dealing with mutually exclusive events. When you calculate the probability of one event or another occurring, and these events cannot happen at the same time, you add their probabilities. This is because the occurrence of one event precludes the occurrence of the other.
However, the complete rule that should be considered is P(A OR B) = P(A) + P(B) − P(A AND B). This equation accounts for cases where A and B are not mutually exclusive. This additional term, P(A AND B), subtracts the probability of both events happening together (if it's possible), which would otherwise be counted twice.
To find the probability of two or more independent events occurring together, which is a different situation, you would instead apply the product rule and multiply the probabilities of the individual events. The key terms here are 'and' for the product rule, and 'or' for the sum rule.
Overall, the probability calculation depends on the relationship between the events in question, whether they are mutually exclusive, independent, or not.