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Chapter 4: Q4 (page 143)
Subjective Probability Estimate the probability that the next time you turn on a light switch, you discover that a bulb does work.
An estimate of the probability that the next time the bulb will glow when the light switch is turned on is equal to 0.998.
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In Exercises 25–32, find the probability and answer the questions. XSORT Gender Selection MicroSort’s XSORT gender selection technique was designed to increase the likelihood that a baby will be a girl. At one point before clinical trials of the XSORT gender selection technique were discontinued, 945 births consisted of 879 baby girls and 66 baby boys (based on data from the Genetics & IVF Institute). Based on these results, what is the probability of a girl born to a couple using MicroSort’s XSORT method? Does it appear that the technique is effective in increasing the likelihood that a baby will be a girl?
In Exercises 21–24, use these results from the “1-Panel-THC” test for marijuana use, which is provided by the company Drug Test Success: Among 143 subjects with positive test results, there are 24 false positive results; among 157 negative results, there are 3 false negative results. (Hint: Construct a table similar to Table 4-1, which is included with the Chapter Problem.)
Testing for Marijuana Use If one of the test subjects is randomly selected, find the probability that the subject tested negative or used marijuana.
In Exercises 9–20, use the data in the following table, which lists drive-thru order accuracy at popular fast food chains (data from a QSR Drive-Thru Study). Assume that orders are randomly selected from those included in the table.
McDonald’s | Burger King | Wendy’s | Taco Bell | |
Order Accurate | 329 | 264 | 249 | 145 |
OrderNotAccurate | 33 | 54 | 31 | 13 |
Fast Food Drive-Thru Accuracy If one order is selected, find the probability of getting an order from McDonald’s or an order that is accurate. Are the events of selecting an order from McDonald’s and selecting an accurate order disjoint events?
In Exercises 21–24, refer to the sample data in Table 4-1, which is included with the Chapter Problem. Assume that 1 of the 555 subjects included in Table 4-1 is randomly selected.
Positive Test Result (Test shows drug use) | Negative Test Result (Test shows no drug use) | |
Subject Uses Drugs | 45 (True Positive) | 5 (False Negative) |
Subject Does Not Use drugs | 25 (False Positive) | 480 (True Negative) |
Drug Testing Job Applicants Find the probability of selecting someone who does not use drugs. Does the result appear to be reasonable as an estimate of the proportion of the adult population that does not use drugs?
In Exercises 17–20, refer to the accompanying table showing results from a Chembio test for hepatitis C among HIV-infected patients (based on data from a variety of sources).
Positive Test Result | Negative Test Result | |
Hepatitis C | 335 | 10 |
No Hepatitis C | 2 | 1153 |
False Positive Find the probability of selecting a subject with a positive test result, given that the subject does not have hepatitis C. Why is this case problematic for test subjects?
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