Bayes\' Theorem You are given two sets of raffle tickets, both of which contain
ID: 3320455 • Letter: B
Question
Bayes' Theorem You are given two sets of raffle tickets, both of which contain winners. You can select 4 tickets from either one pile or the other, but not both. Your initial chan 20%. Your chance of having selected a ticket chance of having selected a ticket from set 1 given that it is a winner is 35%. Likewise, your chance of having selected a ticket from set 1 given that it is not a winner 60%. Determine the probability of having a winning ticket given that you have selected all four tickets from set 1. from set 2 given that it is a winner is 40% and yourExplanation / Answer
By Bayes theorem we know that
P(A given B) or P(A | B) = P(A B)/P(B)
Given that
i)P(getting a winning ticket) or P( slected a winning ticket) = 0.2 or 20%
ii) P(selected a ticket from set 2 given that it is a winner) = 0.35 or 35%
P(selected from set 2 | slected a winning ticket) = 0.35
P(selected from set 2 and slected a winning ticket)/P( slected a winning ticket) = 0.35
P(selected from set 2 and slected a winning ticket) = 0.35*P( slected a winning ticket) = 0.35*0.2 = 0.07
we alseo know that P( slected a winning ticket) = P(selected from set 1 and slected a winning ticket)+ P(selected from set 2 and slected a winning ticket)
so P(selected from set 1 and slected a winning ticket) = 0.2-0.07 = 0.13
iii)P(selected a ticket from set 1 given that it is not a winner) = 0.6 or 60%
P(selected from set 1 and slected a non winning ticket)/P( slected a winning ticket) = 0.60
P(selected from set 1 and slected a non winning ticket) = 0.60*P( slected a non winning ticket) = 0.60*(1-0.2) = 0.48
P(selected from set 1) = P(selected from set 1 and slected a winning ticket) +P(selected from set 1 and slected a non winning ticket) = 0.13+0.48 = 0.61
By Bayes theorem
probability of having a winning ticket given that you have selected all four tickets from set 1 =
P(selected from set 1 and slected a winning ticket)/P(selected from set 1)
= 0.13/0.61 = 0.2131
so probability of having a winning ticket given that you have selected all four tickets from set 1 is 0.2131
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