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Unformatted text preview: ical records show that over the past 8 years 70 percent of the accounts
have been current. Determine the sample size needed in order to be 99% confident that the
sample proportion of the current customer accounts is within .03 of the true proportion of all
current accounts for this company.
A. 1842
B. 1548
C. 897
D. 632
E. 1267 40. In a manufacturing process, we are interested in measuring the average length of a certain
type of bolt. Past data indicates that the standard deviation is .25 inches. How many bolts
should be sampled in order to make us 95% confident that the sample mean bolt length is
within .02 inches of the true mean bolt length?
A. 25
B. 49
C. 423
D. 601
E. 1225 1620 Chapter 01  An Introduction to Business Statistics 41. In a manufacturing process, we are interested in measuring the average length of a certain
type of bolt. Based on a preliminary sample of 9 bolts, the sample standard deviation is .3
inches. How many bolts should be sampled in order to make us 95% confident that the sample
mean bolt length is within .02 inches of the true mean bolt length?
A. 865
B. 80
C. 1470
D. 3989
E. 1197 42. A company is interested in estimating
, the mean number of days of sick leave taken
by its employees. The firm's statistician randomly selects 100 personnel files and notes the
number of sick days taken by each employee. The sample mean is 12.2 days and the sample
standard deviation is 10 days. Calculate a 93% confidence interval for
, the mean number
of days of sick leave.
A. [10.725 13.675]
B. [10.390 14.010]
C. [12.019 12.381]
D. [12.053 12.348]
E. [11.735 12.665] 43. A company is interested in estimating
, the mean number of days of sick leave taken
by its employees. The firm's statistician randomly selects 100 personnel files and notes the
number of sick days taken by each employee. The sample mean is 12.2 days and the sample
standard deviation is 10 days. How many personnel files would the director have to select in
order to estimate µ to within 2 days with a 99% confidence interval?
A. 2
B. 13
C. 136
D. 165
E. 166 1621 Chapter 01  An Introduction to Business Statistics 44. The state highway department is studying traffic patterns on one of the busiest highways
in the state. As part of the study, the department needs to estimate the average number of
vehicles that pass an intersection each day. A random sample of 64 days gives us a sample
mean of 14,205 cars and a sample standard deviation of 1,010 cars. What is the 92%
confidence interval estimate of µ, the mean number of cars passing the intersection?
A. [12,438 15,972]
B. [14,028 14,382]
C. [12,189 14,221]
D. [13,984 14,426]
E. [14,183 14,227] 45. The state highway department is studying traffic patterns on one of the busiest highways
in the state. As part of the study, the department needs to estimate the average number of
vehicles that pass an intersection each day. A random sample of 64 days gives us a sample
mean of 14,205 cars and a sample standard deviation of 1,010 cars. After calculating the
confidence interval, the highway department officials decide that the precision is too low for
their needs. They feel the precision should be 300 cars. Given this precision, and needing to
be 99% confident, how many days do they need to sample?
A. 109
B. 76
C. 75
D. 62
E. 9 46. The U.S. Department of Health and Human Services collected sample data for 772 males
between the ages of 18 and 24. That sample group has a mean height of 69.7 inches with a
standard deviation of 2.8 inches. Find the 99% confidence interval for the mean height of all
males between the ages of 18 and 24.
A. [63.19 76.21]
B. [62.49 76.91]
C. [69.65 69.75]
D. [69.47 69.93]
E. [69.44 69.96] 1622 Chapter 01  An Introduction to Business Statistics 47. In a study of factors affecting soldiers' decisions to reenlist, 320 subjects were measured
for an index of satisfaction and the sample mean is 28.8 and the sample standard deviation is
7.3. Use the given sample data to construct the 98% confidence interval for the population
mean.
A. [27.85 29.75]
B. [27.96 29.64]
C. [11.82 45.78]
D. [28.75 28.85]
E. [28.60 29.00] 48. A psychologist is collecting data on the time it takes to learn a certain task. For 50
randomly selected adult subjects, the sample mean is 16.40 minutes and the sample standard
deviation is 4.00 minutes. Construct the 95% confidence interval for the mean time required
by all adults to learn the task.
A. [8.56 24.24]
B. [15.47 17.33]
C. [16.24 16.56]
D. [15.29 17.51]
E. [17.12 48.48] 49. Research has been conducted that studies the role that the age of workers has in
determining the hours per month spent on personal tasks. A sample of 1,686 adults were observed for one month. The data are:
Construct a 98% confidence interval for the mean hours spent on personal tasks for 2544
year olds.
A. [3.96 4.12]
B. [3.97 4.11]
C. [3.98 4.10]
D. [2.16 5.92]
E. [3.95 4.13] 1623 Chapter 01  An Introduction to Business Statistics 50. Unoccupied seats on flights cause airli...
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 Winter '14

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