The probability of rain is . If it rains, the chance a bus is late is ; if it does not rain, the chance is . What is the probability that the bus is not late?
Answer and explanation
Correct answer: D.
- Step 1: Rain and not late: .
- Step 2: Dry and not late: .
- Step 3: Add the two ways: .
Answer
.
Why not the others: : is the probability that the bus is late. : counts only the dry-weather branch. : counts only the rainy-weather branch.
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