INSTRUCTOR ANSWER GUIDE
OpenStax Introductory Business Statistics 2e
Instructor Answer Guide
,OpenStax Introductory Business Statistics 2e
Instructor Answer Guide
CHAPTER 8: CONFIDENCE INTERVALS
Exercise 1. A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Identify the following:
a. x = ____
b. sx = ____
c. n = ____
d. n – 1 = ____
Solution
a. x = 1.5
b. sx = 0.5
c. n = 70
d. n – 1 = 69
Exercise 2.
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Define the random variables X and X , in words.
Solution
X is the number of hours a patient waits in the emergency room
before being called back to be examined. X is the mean wait time of
70 patients in the emergency room.
Exercise 3.
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Which distribution should you use for this problem?
Solution
Student’s t: t69
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October 28, 2025
,OpenStax Introductory Business Statistics 2e
Instructor Answer and Solution Guide
Chapter 8: Confidence Intervals
Exercise 4
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Construct a 95% confidence interval for the population mean time
spent waiting. State the confidence interval, sketch the graph, and
calculate the error bound.
Solution CI: (1.3808, 1.6192)
Figure 8.12
EBM = 0.12
Exercise 5.
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Explain in complete sentences what the confidence interval means.
Solution
We are 95% confident that the population mean waiting time is
between 1.38 hours and 1.62 hours for patients in the emergency
room before getting called back to be examined.
Exercise 6.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Identify the following:
a. x = ____
b. sx = ____
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October 28, 2025
, OpenStax Introductory Business Statistics 2e
Instructor Answer Guide
c. n = ____
d. n – 1 = ____
Solution a. x = 151
b. sx = 32
c. n = 108
d. n – 1 = 107
Exercise 7.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Define the random variable X in words.
Solution X is the number of hours per month an American watches television.
Exercise 8.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Define the random variable X in words.
Solution
X is the mean number of hours spent watching television per month
from a sample of 108 Americans.
Exercise 9.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Which distribution should you use for this problem?
Solution Student’s t: t107
Exercise 10.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
4
October 28, 2025
OpenStax Introductory Business Statistics 2e
Instructor Answer Guide
,OpenStax Introductory Business Statistics 2e
Instructor Answer Guide
CHAPTER 8: CONFIDENCE INTERVALS
Exercise 1. A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Identify the following:
a. x = ____
b. sx = ____
c. n = ____
d. n – 1 = ____
Solution
a. x = 1.5
b. sx = 0.5
c. n = 70
d. n – 1 = 69
Exercise 2.
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Define the random variables X and X , in words.
Solution
X is the number of hours a patient waits in the emergency room
before being called back to be examined. X is the mean wait time of
70 patients in the emergency room.
Exercise 3.
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Which distribution should you use for this problem?
Solution
Student’s t: t69
2
October 28, 2025
,OpenStax Introductory Business Statistics 2e
Instructor Answer and Solution Guide
Chapter 8: Confidence Intervals
Exercise 4
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Construct a 95% confidence interval for the population mean time
spent waiting. State the confidence interval, sketch the graph, and
calculate the error bound.
Solution CI: (1.3808, 1.6192)
Figure 8.12
EBM = 0.12
Exercise 5.
A hospital is trying to cut down on emergency room wait times. It is
interested in the amount of time patients must wait before being
called back to be examined. An investigation committee randomly
surveyed 70 patients. The sample mean was 1.5 hours with a sample
standard deviation of 0.5 hours.
Explain in complete sentences what the confidence interval means.
Solution
We are 95% confident that the population mean waiting time is
between 1.38 hours and 1.62 hours for patients in the emergency
room before getting called back to be examined.
Exercise 6.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Identify the following:
a. x = ____
b. sx = ____
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October 28, 2025
, OpenStax Introductory Business Statistics 2e
Instructor Answer Guide
c. n = ____
d. n – 1 = ____
Solution a. x = 151
b. sx = 32
c. n = 108
d. n – 1 = 107
Exercise 7.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Define the random variable X in words.
Solution X is the number of hours per month an American watches television.
Exercise 8.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Define the random variable X in words.
Solution
X is the mean number of hours spent watching television per month
from a sample of 108 Americans.
Exercise 9.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
population distribution is normal.
Which distribution should you use for this problem?
Solution Student’s t: t107
Exercise 10.
One hundred eight Americans were surveyed to determine the
number of hours they spend watching television each month. It was
revealed that they watched an average of 151 hours each month with
a standard deviation of 32 hours. Assume that the underlying
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October 28, 2025
