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Which expression is the addition rule for two events A and B?
AP(A or B) = P(A) + P(B) + P(A and B)
BP(A or B) = P(A) times P(B) in all cases
CP(A or B) = P(A) + P(B) when B follows A
DP(A or B) = P(A) + P(B) minus P(A and B)
Answer & Solution
Correct answer: D. P(A or B) = P(A) + P(B) minus P(A and B)
1. The word or points to the union of the two events.
2. Adding the two probabilities counts every shared outcome twice.
3. Subtracting the joint probability removes that double count, giving P(A) plus P(B) minus P(A and B).
_Source: OpenStax Introductory Business Statistics (CC BY 4.0), Ch 3 "Probability Topics", section 3.3 Two Basic Rules of Probability_
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