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File: Ch08, Chapter 8: Statistical Inference: Estimation for Single Populations
True/False
1. When a statistic calculated from sample data is used to estimate a population parameter, it is
called a point estimate.
Ans: True
Response: See section 8.1 Estimating the Population Mean using the z Statistic (Known)
Difficulty: Easy
2. When a range of values is used to estimate a population parameter, it is called a range
estimate.
Ans: False
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Easy
3. If the population is not normal but its standard deviation,  is known and the sample size, n is
large (n ≥ 30), z-distribution values may be used to determine interval estimates for the
population mean.
Ans: True
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
4. If the population is normal and its standard deviation, , is known but the sample size is small,
z-distribution values may not be used to determine interval estimates for the population mean.
Ans: False
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
5. When the population standard deviation, , is unknown the sample standard deviation, s, is
used in determining the interval estimate for the population mean.
Ans: True
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
6. If the population is normal and its standard deviation, , is known and the sample size, n, is
large (n ≥ 30), interval estimates for the population mean must be determined using z-values.
Ans: True
Response: See section 8.1 Estimating the Population Mean using the z Statistic (
Known)Difficulty: Medium
7. An assumption underlying the use of t-statistic in sample-based estimation is that the
population is normally distributed.
Ans: True
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
8. A t-distribution is similar to a normal distribution, but with flatter tails.
Ans: True
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Easy
9. In order to find values in the t distribution table, you must determine the appropriate degrees of
freedom based on the sample sizes.
Ans: True
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Easy
10. If the degrees of freedom in a t distribution increase, difference between the t values and the z
values will also increase.
Ans: False
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
11. In determining the interval estimates for a population proportion using the sample proportion,
it is appropriate to use the values from a t-distribution rather than the z-distribution.
Ans: False
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
12. In determining the interval estimates for a population variance using the sample variance, it is
appropriate to use the values from a chi-square distribution rather than a t-distribution.
Ans: True
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
13. In estimating the sample size necessary to estimate a population mean, the error of
estimation, E, is equal to the difference between the sample mean and the population mean
Ans: True
Response: See section 8.5 Estimating the Sample Variance
Difficulty: Medium
14. Use of the chi-square statistic to estimate the population variance is extremely robust to the
assumption that the population is normally distributed.
Ans: False
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
15. Like a t-distribution, a chi-square distribution is symmetrical and extends from minus infinity
to plus infinity.
Ans: False
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
Multiple Choice
16. Catherine Chao, Director of Marketing Research, is evaluating consumer acceptance of a new
toothpaste package. Her staff reports that 17% of a random sample of 200 households prefers the
new package to all other package designs. If Catherine concludes that 17% of all households
prefer the new package, she is using a _______.
a) a point estimate
b) a range estimate
c) a statistical parameter
d) an interval estimate
e) an exact estimate
Ans: a
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
17. Brian Vanecek, VP of Operations at Portland Trust Bank, is evaluating the service level
provided to walk-in customers. Accordingly, his staff recorded the waiting times for 45 randomly
selected walk-in customers, and calculated that their mean waiting time was 15 minutes. If Brian
concludes that the average waiting time for all walk-in customers is 15 minutes, he is using a
________.
a) a range estimate
b) a statistical parameter
c) an interval estimate
d) a point estimate
e) an exact estimate
Ans: d
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
18. Eugene Gates, Marketing Director of Mansfield Motors Manufacturers, Inc.’s Electrical
Division, is leading a study to assess the relative importance of product features. An item on a
survey questionnaire distributed to 100 of Mansfield’s customers asked them to rate the
importance of “ease of maintenance” on a scale of 1 to 10 (with 1 meaning “not important” and
10 meaning “highly important”). His staff assembled the following statistics.
Ease of Maintenance
Mean
7.5
Standard Deviation
1.5
If Eugene concludes that the average rate of “ease of maintenance” for all customers is 7.5, he is
using ________.
a) a range estimate
b) a statistical parameter
c) a point estimate
d) an interval estimate
e) a guesstimate
Ans: c
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
19. The z value associated with a two-sided 90% confidence interval is _______.
a) 1.28
b) 1.645
c) 1.96
d) 2.575
e) 2.33
Ans: b
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
20. The z value associated with a two-sided 95% confidence interval is _______.
a) 1.28
b) 1.645
c) 1.96
d) 2.575
e) 2.33
Ans: c
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
21. The z value associated with a two-sided 80% confidence interval is _______.
a) 1.645
b) 1.28
c) 0.84
d) 0.29
e) 2.00
Ans: b
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
22. The z value associated with a two-sided 88% confidence interval is _______.
a) 1.28
b) 1.55
c) 1.17
d) 0.88
e) 1.90
Ans: b
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
23. Suppose a random sample of 36 is selected from a population with a standard deviation of 12.
If the sample mean is 98, the 99% confidence interval to estimate the population mean is
_______.
a) 94.08 to 101.92
b) 92.85 to 103.15
c) 97.35 to 98.65
d) 93.34 to 102.66
e) 90.20 to 105.00
Ans: b
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
24. Suppose a random sample of 36 is selected from a population with a standard deviation of 12.
If the sample mean is 98, the 90% confidence interval for the population mean is _______.
a) 94.71 to 101.29
b) 97.45 to 98.55
c) 94.08 to 101.92
d) 97.35 to 98.65
e) 95.00 to 105.00
Ans: a
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
25. Suppose a random sample of size 64 is selected from a population yielding a sample mean of
26. The population standard deviation is 4. From this information, the 90% confidence interval
to estimate the population mean can be computed to be _______.
a) 25.36 to 26.64
b) 25.92 to 26.08
c) 25.18 to 26.82
d) 25.90 to 26.10
e) 26.00 to 27.80
Ans: c
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
26. Brian Vanecek, VP of Operations at Portland Trust Bank, is evaluating the service level
provided to walk-in customers. Accordingly, his staff recorded the waiting times for 64
randomly selected walk-in customers and determined that their mean waiting time was 15
minutes. Assume that the population standard deviation is 4 minutes. The 90% confidence
interval for the population mean of waiting times is ________.
a) 14.27 to 15.73
b) 14.18 to 15.82
c) 9.88 to 20.12
d) 13.86 to 16.14
e) 18.12 to 19.87
Ans: b
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
27. Brian Vanecek, VP of Operations at Portland Trust Bank, is evaluating the service level
provided to walk-in customers. Accordingly, his staff recorded the waiting times for 64
randomly selected walk-in customers and determined that their mean waiting time was 15
minutes. Assume that the population standard deviation is 4 minutes. The 95% confidence
interval for the population mean of waiting times is ________.
a) 14.02 to 15.98
b) 7.16 to 22.84
c) 14.06 to 15.94
d) 8.42 to 21.58
e) 19.80 to 23.65
Ans: a
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
28. James Desreumaux, VP of Human Resources of American First Banks (AFB), is reviewing
the employee training programs of AFB banks. His staff randomly selected personnel files for
100 tellers in the Southeast Region and determined that their mean training time was 25 hours.
Assume that the population standard deviation is 5 hours. The 88% confidence interval for the
population mean of training times is ________.
a) 17.25 to 32.75
b) 24.23 to 25.78
c) 24.42 to 25.59
d) 19.15 to 30.85
e) 21.00 t0 32.00
Ans: b
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
29. James Desreumaux, VP of Human Resources of American First Banks (AFB), is reviewing
the employee training programs of AFB banks. His staff randomly selected personnel files for
100 tellers in the Southeast Region and determined that their mean training time was 25 hours.
Assume that the population standard deviation is 5 hours. The 92% confidence interval for the
population mean of training times is ________.
a) 16.25 to 33.75
b) 24.30 to 25.71
c) 17.95 to 32.05
d) 24.12 to 25.88
e) 24.45 to 27.32
Ans: d
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
30. James Desreumaux, VP of Human Resources of American First Banks (AFB), is reviewing
the employee training programs of AFB banks. His staff randomly selected personnel files for
100 tellers in the Southeast Region and determined that their mean training time was 25 hours.
Assume that the population standard deviation is 5 hours. The 95% confidence interval for the
population mean of training times is ________.
a) 15.20 to 34.80
b) 24.18 to 25.82
c) 24.02 to 25.98
d) 16.78 to 33.23
e) 23.32 to 35.46
Ans: c
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
31. A random sample of 64 items is selected from a population of 400 items. The sample mean is
200. The population standard deviation is 48. From this data, a 95% confidence interval to
estimate the population mean can be computed as _______.
a) 189.21 to 210.79
b) 188.24 to 211.76
c) 190.13 to 209.87
d) 190.94 to 209.06
e) 193.45 to 211.09
Ans: a
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
32. A random sample of 64 items is selected from a population of 400 items. The sample mean is
200. The population standard deviation is 48. From this data, a 90% confidence interval to
estimate the population mean can be computed as _______.
a) 189.21 to 210.79
b) 188.24 to 211.76
c) 190.13 to 209.87
d) 190.94 to 209.06
e) 193.45 to 211.09
Ans: d
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
33. The normal distribution is used to test about a population mean for large samples if the
population standard deviation is known. "Large" is usually defined as _______.
a) at least 10
b) at least 5% of the population size
c) at least 30
d) at least 12
e) at least 100
Ans: c
Response: See section 8.1 Estimating the Population Mean using the z Statistic ( Known)
Difficulty: Medium
34. The table t value associated with the upper 5% of the t distribution and 12 degrees of freedom
is _______.
a) 2.179
b) 1.782
c) 1.356
d) 3.055
e) 3.330
Ans: b
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Easy
35. The table t value associated with the upper 5% of the t distribution and 14 degrees of freedom
is _______.
a) 2.977
b) 2.624
c) 2.145
d) 1.761
e)
Ans: d
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Easy
36. The table t value associated with the upper 10% of the t distribution and 23 degrees of
freedom is _______.
a) 1.319
b) 1.714
c) 2.069
d) 1.321
e) 2.332
Ans: a
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Easy
37. A researcher is interested in estimating the mean value for a population. She takes a random
sample of 17 items and computes a sample mean of 224 and a sample standard deviation of 32.
She decides to construct a 98% confidence interval to estimate the mean. The degrees of freedom
associated with this problem are _______.
a) 18
b) 17
c) 16
d) 15
e) 20
Ans: c
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Easy
38. The lengths of steel rods produced by a shearing process are normally distributed. A random
sample of 10 rods is selected; the sample mean length is 119.05 inches; and the sample standard
deviation is 0.10 inch. The 95% confidence interval for the population mean rod length is
______________.
a) 118.99 to 119.11
b) 118.82 to 119.28
c) 118.98 to 119.12
d) 118.85 to 119.25
e) 119.89 to 122.12
Ans: c
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
39. The lengths of steel rods produced by a shearing process are normally distributed. A random
sample of 10 rods is selected; the sample mean length is 119.05 inches; and the sample standard
deviation is 0.10 inch. The 90% confidence interval for the population mean rod length is
______________.
a) 118.99 to 119.11
b) 118.87 to 119.23
c) 119.00 to 119.10
d) 118.89 to 119.21
e) 119.21 to 123.87
Ans: a
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
40. The weights of aluminum castings produced by a process are normally distributed. A random
sample of 5 castings is selected; the sample mean weight is 2.21 pounds; and the sample standard
deviation is 0.12 pound. The 98% confidence interval for the population mean casting weight is
_________.
a) 1.76 to 2.66
b) 2.01 to 2.41
c) 2.08 to 2.34
d) 1.93 to 2.49
e) 2.49 to 2.67
Ans: b
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
41. Life tests performed on a sample of 13 batteries of a new model indicated: (1) an average life
of 75 months, and (2) a standard deviation of 5 months. Other battery models, produced by
similar processes, have normally distributed life spans. The 98% confidence interval for the
population mean life of the new model is _________.
a) 63.37 to 86.63
b) 61.60 to 88.41
c) 71.77 to 78.23
d) 71.28 to 78.72
e) 79.86 to 81.28
Ans: d
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
42. Life tests performed on a sample of 13 batteries of a new model indicated: (1) an average life
of 75 months, and (2) a standard deviation of 5 months. Other battery models, produced by
similar processes, have normally distributed life spans. The 90% confidence interval for the
population mean life of the new model is _________.
a) 66.78 to 83.23
b) 72.72 to 77.28
c) 72.53 to 77.47
d) 66.09 to 83.91
e) 73.34 to 76.25
Ans: c
Response: See section 8.2 Estimating the Population Mean using the t Statistic ( Unknown)
Difficulty: Medium
43. A researcher wants to estimate the proportion of the population which possesses a given
characteristic. A random sample of size 800 is taken resulting in 360 items which possess the
characteristic. The point estimate for this population proportion is _______.
a) 0.55
b) 0.45
c) 0.35
d) 0.65
e) 0.70
Ans: b
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
44. A researcher wants to estimate the proportion of the population which possesses a given
characteristic. A random sample of size 1800 is taken resulting in 450 items which possess the
characteristic. The point estimate for this population proportion is _______.
a) 0.55
b) 0.45
c) 0.35
d) 0.25
e) 0.15
Ans: d
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
45. A researcher wants to estimate the proportion of a population which possesses a given
characteristic. A random sample of size 250 is taken and 40% of the sample possesses the
characteristic. The 90% confidence interval to estimate the population proportion is ____.
a) 0.35 to 0.45
b) 0.34 to 0.46
c) 0.37 to 0.43
d) 0.39 to 0.41
e) 0.40 to 0.45
Ans: a
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
46. A researcher wants to estimate the proportion of a population which possesses a given
characteristic. A random sample of size 250 is taken and 40% of the sample possesses the
characteristic. The 95% confidence interval to estimate the population proportion is _______.
a) 0.35 to 0.45
b) 0.34 to 0.46
c) 0.37 to 0.43
d) 0.39 to 0.41
e) 0.40 to 0.42
Ans: b
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
47. A researcher wants to estimate the proportion of a population which possesses a given
characteristic. A random sample of size 200 is taken and 30% of the sample possesses the
characteristic. The 95% confidence interval to estimate the population proportion is _______.
a) 0.53 to 0.67
b) 0.25 to 0.35
c) 0.24 to 0.36
d) 0.27 to 0.33
e) 0.28 to 0.34
Ans: c
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
48. A researcher wants to estimate the proportion of a population which possesses a given
characteristic. A random sample of size 200 is taken and 30% of the sample possesses the
characteristic. The 90% confidence interval to estimate the population proportion is _______.
a) 0.53 to 0.67
b) 0.25 to 0.35
c) 0.24 to 0.36
d) 0.27 to 0.33
e) 0.33 to 0.39
Ans: b
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
49. A random sample of 225 items from a population results in 60% possessing a given
characteristic. Using this information, the researcher constructs a 99% confidence interval to
estimate the population proportion. The resulting confidence interval is _______.
a) 0.54 to 0.66
b) 0.59 to 0.61
c) 0.57 to 0.63
d) 0.52 to 0.68
e) 0.68 to 0.76
Ans: d
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
50. A random sample of 225 items from a population results in 60% possessing a given
characteristic. Using this information, the researcher constructs a 90% confidence interval to
estimate the population proportion. The resulting confidence interval is _______.
a) 0.546 to 0.654
b) 0.536 to 0.664
c) 0.596 to 0.604
d) 0.571 to 0.629
e) 0.629 to 0.687
Ans: a
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
51. Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business
communications. A random sample of 200 e-mail messages was selected. Thirty of the
messages were not business related. The point estimate for this population proportion is
_______.
a) 0.150
b) 0.300
c) 0.182
d) 0.667
e) 0.786
Ans: a
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
52. Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business
communications. A random sample of 200 e-mail messages was selected. Thirty of the
messages were not business related. The 90% confidence interval for the population proportion is
_________.
a) 0.108 to 0.192
b) 0.153 to 0.247
c) 0.091 to 0.209
d) 0.145 to 0.255
e) 0.255 to 0.265
Ans: a
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
53. Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business
communications. A random sample of 200 e-mail messages was selected. Thirty of the
messages were not business related. The 95% confidence interval for the population proportion is
_________.
a) 0.108 to 0.192
b) 0.153 to 0.247
c) 0.091 to 0.209
d) 0.101 to 0.199
e) 0.199 to 0.201
Ans: d
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
54. Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business
communications. A random sample of 200 e-mail messages was selected. Thirty of the
messages were not business related. The 98% confidence interval for the population proportion is
_________.
a) 0.108 to 0.192
b) 0.153 to 0.247
c) 0.091 to 0.209
d) 0.145 to 0.255
e) 0.250 to 0.275
Ans: c
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
55. Catherine Chao, Director of Marketing Research, is evaluating consumer acceptance of a new
toothpaste package. She randomly selects a sample of 200 households. Forty households prefer
the new package to all other package designs. The point estimate for this population proportion
is _______.
a) 0.20
b) 0.25
c) 0.40
d) 0.45
e) 0.55
Ans: a
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
56. Catherine Chao, Director of Marketing Research, is evaluating consumer acceptance of a new
toothpaste package. She randomly selects a sample of 200 households. Forty households prefer
the new package to all other package designs. The 90% confidence interval for the population
proportion is _________.
a) 0.199 to 0.201
b) 0.153 to 0.247
c) 0.164 to 0.236
d) 0.145 to 0.255
e) 0.185 to 0.275
Ans: b
Response: See section 8.3 Estimating the Population Proportion
Difficulty: Medium
57. Brian Vanecek, VP of Operations at Portland Trust Bank, is evaluating the service level
provided to walk-in customers. Brian would like to minimize the variance of waiting time for
these customers, since this would mean each customer received the same level of service.
Accordingly, his staff recorded the waiting times for 15 randomly selected walk-in customers,
and determined that their mean waiting time was 15 minutes and that the standard deviation was
4 minutes. Assume that waiting time is normally distributed. The 90% confidence interval for
the population variance of waiting times is ________.
a) 9.46 to 34.09
b) 56.25 to 64.87
c) 11.05 to 16.03
d) 8.58 to 39.79
e) 12.50 to 42.35
Ans: a
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
58. Brian Vanecek, VP of Operations at Portland Trust Bank, is evaluating the service level
provided to walk-in customers. Brian would like to minimize the variance of waiting time for
these customers, since this would mean each customer received the same level of service.
Accordingly, his staff recorded the waiting times for 15 randomly selected walk-in customers,
and determined that their mean waiting time was 15 minutes and that the standard deviation was
4 minutes. Assume that waiting time is normally distributed. The 95% confidence interval for
the population variance of waiting times is ________.
a) 9.46 to 34.09
b) 56.25 to 64.87
c) 11.05 to 16.03
d) 8.58 to 39.79
e) 12.50 to 42.35
Ans: d
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
59. Velma Vasquez, fund manager of the Vasquez Value Fund, manages a portfolio of 250
common stocks. Velma relies on various statistics, such as variance, to assess the overall risk of
stocks in an economic sector. Her staff reported that for a sample 14 utility stocks the mean
annualized return was 14% and that the variance was 3%. Assume that annualized returns are
normally distributed. The 90% confidence interval for the population variance of annualized
returns is _______.
a) 0.018 to 0.064
b) 0.016 to 0.078
c) 0.017 to 0.066
d) 0.016 to 0.075
e) 0.020 to 0.080
Ans: c
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
60. Velma Vasquez, fund manager of the Vasquez Value Fund, manages a portfolio of 250
common stocks. Velma relies on various statistics, such as variance, to assess the overall risk of
stocks in an economic sector. Her staff reported that for a sample 14 utility stocks the mean
annualized return was 14% and that the variance was 3%. Assume that annualized returns are
normally distributed. The 95% confidence interval for the population variance of annualized
returns is _______.
a) 0.018 to 0.064
b) 0.016 to 0.078
c) 0.017 to 0.066
d) 0.016 to 0.075
e) 0.020 to 0.080
Ans: b
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
61. James Desreumaux, VP of Human Resources of American First Banks (AFB), is reviewing
the employee training programs of AFB banks. His staff randomly selected personnel files for 10
tellers in the Southwest Region, and determined that their mean training time was 25 hours and
that the standard deviation was 5 hours. Assume that training times are normally distributed.
The 90% confidence interval for the population variance of training times is ________.
a) 11.83 to 83.33
b) 2.37 to 16.67
c) 2.66 to 13.51
d) 13.30 to 67.57
e) 15.00 to 68.00
Ans: d
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
62. James Desreumaux, VP of Human Resources of American First Banks (AFB), is reviewing
the employee training programs of AFB banks. His staff randomly selected personnel files for 10
tellers in the Southwest Region, and determined that their mean training time was 25 hours and
that the standard deviation was 5 hours. Assume that training times are normally distributed.
The 95% confidence interval for the population variance of training times is ________.
a) 11.83 to 83.33
b) 2.37 to 16.67
c) 2.66 to 13.51
d) 13.30 to 67.57
e) 15.40 to 68.28
Ans: a
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
63. Given n = 17, s2 = 18.56, and that the population is normally distributed, the 80% confidence
interval for the population variance is ________.
a) 11.4372   2  36.3848
b) 23.5418   2  9.31223
c) 12.6141   2  31.8892
d) 11.2929   2  37.2989
e) 14.2929   2  39.2989
Ans: c
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
64. Given n = 12, s2 = 44.90, and that the population is normally distributed, the 99% confidence
interval for the population variance is ________.
a) 19.0391   2  175.2888
b) 23.0881   2  122.3495
c) 25.6253   2  103.0993
d) 18.4588   2  189.7279
e) 14.2929   2  139.2989
Ans: d
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
65. Given n = 20, s = 32, and that the population is normally distributed, the 90% confidence
interval for the population variance is ________.
a) 645.4458   2  1923.0986
b) 599.3635   2  2135.3859
c) 592.2258   2  2184.4685
d) 652.0129   2  1887.4185
e) 642.0929   2  3982.2989
Ans: a
Response: See section 8.4 Estimating the Population Variance
Difficulty: Medium
66. A researcher wants to determine the sample size necessary to adequately conduct a study to
estimate the population mean to within 5 points. The range of population values is 80 and the
researcher plans to use a 90% level of confidence. The sample size should be at least _______.
a) 44
b) 62
c) 216
d) 692
e) 700
Ans: a
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
67. A study is going to be conducted in which a population mean will be estimated using a 92%
confidence interval. The estimate needs to be within 12 of the actual population mean. The
population variance is estimated to be around 2500. The necessary sample size should be at least
_______.
a) 15
b) 47
c) 53
d) 638
e) 700
Ans: c
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
68. In estimating the sample size necessary to estimate p, if there is no good approximation for
the value of p available, the value of ____ should be used as an estimate of p in the formula.
a) 0.10
b) 0.50
c) 0.40
d) 1.96
e) 2.00
Ans: b
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
69. A researcher wants to estimate the population proportion with a 95% level of confidence. He
estimates from previous studies that the population proportion is no more than .30. The
researcher wants the estimate to have an error of no more than .03. The necessary sample size is
at least _______.
a) 27
b) 188
c) 211
d) 897
e) 900
Ans: d
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
70. Catherine Chao, Director of Marketing Research, is evaluating consumer acceptance of a new
toothpaste package. She plans to use a 95% confidence interval estimate of the proportion of
households which prefer the new packages; she will accept a 0.05 error. Previous studies
indicate that new packaging has an approximately 70% acceptance rate. The sample size should
be at least _______.
a) 27
b) 59
c) 323
d) 427
e) 500
Ans: c
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
71. Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business
communications. He plans to use a 95% confidence interval estimate of the proportion of e-mail
messages that are non-business; he will accept a 0.05 error. Previous studies indicate that
approximately 30% of employee e-mail is not business related. Elwin should sample _______ email messages.
a) 323
b) 12
c) 457
d) 14
e) 100
Ans: a
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
72. Elwin Osbourne, CIO at GFS, Inc., is studying employee use of GFS e-mail for non-business
communications. He plans to use a 98% confidence interval estimate of the proportion of e-mail
messages that are non-business; he will accept a 0.05 error. Previous studies indicate that
approximately 30% of employee e-mail is not business related. Elwin should sample _______ email messages.
a) 323
b) 12
c) 457
d) 14
e) 100
Ans: c
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
73. A researcher wants to estimate the population proportion with a 90% level of confidence.
She estimates from previous studies that the population proportion is no more than .30. The
researcher wants the estimate to have an error of no more than .02. The necessary sample size is
at least _______.
a) 29
b) 47
c) 298
d) 1421
e) 1500
Ans: d
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
74. A study will be conducted to estimate the population proportion. A level of confidence of
99% will be used and an error of no more than .04 is desired. There is no knowledge as to what
the population proportion will be. The size of sample should be at least _______.
a) 1036
b) 160
c) 41
d) 259
e) 289
Ans: a
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
75. A researcher conducts a study to determine what the population proportion is for a given
characteristic. It is believed from previous studies that the proportion of the population will be at
least .65. The researcher wants to use a 98% level of confidence. He also wants the error to be no
more than .03. The sample size should be at least _______.
a) 41
b) 313
c) 1677
d) 1373
e) 1500
Ans: d
Response: See section 8.5 Estimating the Sample Size
Difficulty: Medium
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