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Use the following information to answer the next three exercises: A community college offers classes 6 days a week: Monday through Saturday. Maria conducted a study of the students in her classes to determine how many days per week the students who are in her classes come to campus for classes. In each of her 5 classes she randomly selected 10 students and asked them how many days they come to campus for classes. Each of her classes are the same size.The results of her survey are summarized in [link] .
Number of Days on Campus | Frequency | Relative Frequency | Cumulative Relative Frequency |
---|---|---|---|
1 | 2 | ||
2 | 12 | .24 | |
3 | 10 | .20 | |
4 | .98 | ||
5 | 0 | ||
6 | 1 | .02 | 1.00 |
20 . Combined with convenience sampling, what other sampling technique did Maria use?
21 . How many students come to campus for classes four days a week?
22 . What is the 60 ^{th} percentile for the this data?
Use the following information to answer the next two exercises: The following data are the results of a random survey of 110 Reservists called to active duty to increase security at California airports.
Number of Dependents | Frequency |
---|---|
0 | 11 |
1 | 27 |
2 | 33 |
3 | 20 |
4 | 19 |
23 . Construct a 95% confidence interval for the true population mean number of dependents of Reservists called to active duty to increase security at California airports.
24 . The 95% confidence interval above means:
25 . X ~ U (4, 10). Find the 30 ^{th} percentile.
26 . If X ~ Ex p(0.8), then P ( x < μ ) = __________
27 . The lifetime of a computer circuit board is normally distributed with a mean of 2,500 hours and a standard deviation of 60 hours. What is the probability that a randomly chosen board will last at most 2,560 hours?
28 . A survey of 123 reservists called to active duty as a result of the September 11, 2001, attacks was conducted to determine the proportion that were married. Eighty-six reported being married. Construct a 98% confidence interval for the true population proportion of reservists called to active duty that are married.
29 . Winning times in 26 mile marathons run by world class runners average 145 minutes with a standard deviation of 14 minutes. A sample of the last ten marathon winning times is collected. Let x = mean winning times for ten marathons. The distribution for x is:
30 . Suppose that Phi Beta Kappa honors the top one percent of college and university seniors. Assume that grade point means (GPA) at a certain college are normally distributed with a 2.5 mean and a standard deviation of 0.5. What would be the minimum GPA needed to become a member of Phi Beta Kappa at that college?
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