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Homework Help: Engineering Statistics

  1. May 29, 2009 #1
    1. The problem statement, all variables and given/known data
    A lie detector shows a positive reading 10% of the time given that the person is telling the truth and 95% given the person is lying. Suppose that there is a suspect who is denying the the crime and there is a 50% chance that the person comitted the crime.

    A. what is the probability that the test gives a positive reading?

    B. A test is randomly taken: What is the probability that the person did not commit the crime given that the test indicates a negative reading.

    2. Relevant equations

    3. The attempt at a solution
    A. I did a tree diagram and resulted in summing 10% of 50% and 95% of 50% and received a return of 52.5%. Is this acceptable?

    B. I did another tree diagram and summed the inverse. 90% of 50% and 5% of 50% and received a return of 47.5%
  2. jcsd
  3. May 30, 2009 #2


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    Science Advisor
    Homework Helper

    Hi sisyphus0321! :smile:
    Yup! :biggrin:
    Nope … that's just the probability that the test gives a negative reading.
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