There are two questions in a test. The probability that David answers
the first question correctly is 1/4 and the probability that David
answers the second question correctly is 1/3. Given that David
answers at least one question correctly in the test, find the probability
that he answers the second question correctly.
F.5 Maths
2009-04-16 12:25 am
回答 (1)
2009-04-16 12:58 am
✔ 最佳答案
P(E)
=P(Q1 correct or wrong ,Q2 correct) / P(at least 1Q correct)
= (1 * 1/3) / [1 - P(all wrong)]
= (1/3) / [1 - (1-1/4) (1-1/3)]
= (1/3) / (1/2)
= 2/3
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