Conditional ProbabilityDate: 05/25/2000 at 17:33:01 From: Faraz Sultan Subject: Probability and Logic Hi Dr. Math. I'm going crazy over this problem I haven't been able to figure out - please help. Suppose used car salesmen tell the truth 2/5 of the time, and 1/3 of the trees in a forest are oak. If 4 used car salesmen say that a certain tree in the forest is oak, what is the probability that the tree is indeed oak? I thought the answer would be [(2/5)^4]*[1/3], but that gave me an incorrect answer. (Answer ~= .08989) Please show me how this can be determined. Thanks a lot, Faraz Date: 05/25/2000 at 19:19:09 From: Doctor Anthony Subject: Re: Probability and Logic Hi Faraz: Oak Not oak Prob = 1/3 Prob = 2/3 ------------------------------------------- (1/3).C(4,4)(2/5)^4 (2/3).C(4,0)(3/5)^4 4 say it is oak = 16/1875 162/1875 Total = 178/1875 Probability that we are in the first column 16/1875 16 8 = -------- = --- = -- = 0.08988764 178/1875 178 89 and so probability that it is oak = 8/89 - Doctor Anthony, The Math Forum http://mathforum.org/dr.math/ |
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