which of the following statements best describes the addition rule of probability?
The addition rule of probability says that the probability that event A or event B occurs equals the sum of their individual probabilities minus the probability that they both occur together.
Core idea
- Formally, the general addition rule is
P(A or B)=P(A)+P(B)−P(A and B)P(A\text{ or }B)=P(A)+P(B)-P(A\text{ and }B)P(A or B)=P(A)+P(B)−P(A and B).
- This rule ensures that any overlap (outcomes counted in both A and B) is not double-counted, so that the final probability is correct.
Special case: mutually exclusive events
- If A and B are mutually exclusive (cannot happen at the same time), then P(A and B)=0P(A\text{ and }B)=0P(A and B)=0, so the rule simplifies to P(A or B)=P(A)+P(B)P(A\text{ or }B)=P(A)+P(B)P(A or B)=P(A)+P(B).
- In words: for mutually exclusive events, the addition rule says the probability of A or B is just the sum of their probabilities.
How to recognize it in options
The best description among answer choices will usually look like:
“The probability that A or B occurs equals the probability of A plus the probability of B minus the probability that A and B occur together.”
This wording captures the general addition rule of probability, including the overlap term.
TL;DR:
The correct statement is the one that says:
P(A or B) = P(A) + P(B) − P(A and B).
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