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9. ol Suppose that, based on past experience, it is known that a lie detector te

ID: 3320191 • Letter: 9

Question

9. ol Suppose that, based on past experience, it is known that a lie detector test will indicate innocent person is guilty with probability 08, wh that an ile the test will indicate that a guilty person is innocent with probability 15. Suppose further that 10% of the population under study has committed a traffic violation. If a lie detector test indicates that a randomly chosen individual form this population has committed a traffic violation, what is the probability that this person is innocent of committing a traffic violation?

Explanation / Answer

probabiliy that test comes positive =P(commited violation and positive+not commited violation and positive)

=0.1*(1-0.15)+0.9*0.08=0.157

hence probability that peson is innocent given test is positive =P(not commited violation and positive)/P(positive)

=0.9*0.08/0.157 =0.4586