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Answers for “为什么在计算两个事件的并集概率时要减去交集?”

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Understand why

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We subtract the intersection because adding the individual probabilities P(E)P(E) and P(F)P(F) counts the overlapping region twice. Subtracting P(E∩F)P(E \cap F) once corrects this double-counting so that every outcome in the union is counted exactly once.

Conditions: E and F are overlapping events in a probability space.

Meet the concept

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The union of two events, denoted E∪FE \cup F, means that at least one of the events occurs. It is an inclusive 'or', meaning it includes the case where both E and F happen simultaneously.

Conditions: E and F are events in a probability space.

Know when to use it

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The inclusion-exclusion principle should be used when considering two events that are allowed to have overlap, meaning they can occur together. It is not the relevant setup for mutually exclusive events, where the intersection is empty and the events cannot occur simultaneously.

Conditions: There are two events under consideration.; The events can occur together (their intersection is not empty).