# 4 ProbabilityIn Exercises 17-20, refer to the accompanying table showing results from a Chembio testfor hepatitis C among HIV-infected patients (based on data from a variety of sources).Negative Test ResultPositive Test Result10335Hepatitis C1153No Hepatitis C217. False Pos itive Find the probability of selecting a subject with a positive test result, giventhat the subject does not have hepatitis C. Why is this case problematic for test subjects?18. False Negative Find the probability of selecting a subject with a negative test result, givenhat the subject has hepatitis C. What would be an unfavorable consequence of this error?19. Positive Predictive Value Find the positive predictive value for the test. That is, find theprobability that a subject has hepatitis C, given that the test yields a positive result. Does theresult make the test appear to be effective?20. Negative Predictive Value Find the negative predictive value for the test. That is, find theprobability that a subject does not have hepatitis C, given that the test yields a negative result.Does the result make the test appear to be effective?21. Redundancy in Computer Hard Drives Assume that there is a 3% rate of disk drive fail-ures in a year (based on data from various sources including lifehacker.com)a. If all of your computer data is stored on a hard disk drive with a copy stored on a secondhard disk drive, what is the probability that during a year, you can avoid catastrophe with aleast one working drive? Express the result with four decimal placesb. If copies of all of your computer data are stored on three independent hard disk drives, whais the probability that during a year, you can avoid catastrophe with at least one working driveExpress the result with six decimal places. What is wrong with using the usual round-off rulfor probabilities in this case?22. Redundancy in Stadium Generators Large stadiums rely on backup generators to provide electricity in the event of a power failure. Assume that emergency backup generators fa22 of the times when they are needed (based on data from Arshad Mansoor, senior vice presdent with the Electric Power Research Institute). A stadium has three backup generators so thpower is available if at least one of them works in a power failure. Find the probability of haing at least one of the backup generators working given that a power failure has occurred. Dothe result appear to be adequate for the stadium's needs?23. Composite Drug Test Based on the data in Table 4-1 on page 162, assume that the proability of a randomly selected person testing positive for drug use is 0.126. If drug screenisamples are collected from 5 random subjects and comhinn

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