# A random sample of 20 items is selected from a population. To determine the appropriate t-value

uestion

Question 1

A random sample of 20 items is selected from a population. To determine the appropriate t-value what number of degrees of freedom should be used?

20

19

21

25

.

5 points

Question 2

A federal bank examiner is interested in estimating the mean outstanding defaulted loans balance of all defaulted loans over the last three years. A random sample of 20 defaulted loans yielded a mean of $67,918 with a standard deviation of $16,552.40. Calculate a 90% confidence interval for the mean balance of defaulted loans over the past three years. Round your answer to the next whole number

[66,487 69,349]

[39,299 96,537]

[57,329 78,507]

[61,829 74,007]

[61,519 74,317]

.

5 points

Question 3

A group of statistics students decided to conduct a survey at their university to find the average (mean) amount of time students spent studying per week. They sampled 240 students and found a mean of 22.3 hours per week. Assuming a population standard deviation of 6 hours, what is the 99% level of confidence?

[21.80, 22.80]

[16.3, 28.3]

[21.30, 23.30]

[20.22, 22.0]

.

5 points

Question 4

A random sample of 42 college graduates revealed that they worked an average of 5.5 years on the job before being promoted. The sample standard deviation was 1.1 years. Using the 0.99 degree of confidence, what is the confidence interval for the population mean?

5.04 and 5.96

5.06 and 5.94

2.67 and 8.33

4.40 and 6.60

.

5 points

Question 5

A random sample of 85 group leaders and supervisors revealed that they worked an average of 6.5 years before being promoted. The population standard deviation was 1.7 years. Using the 95% degree of confidence, what is the confidence interval for the population mean?

6.99 and 7.99

4.15 and 7.15

6.14 and 6.86

6.49 and 7.49

.

5 points

Question 6

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 _________ .

44

62

216

692

700

.

5 points

Question 7

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 __________ .

0.35 to 0.45

0.34 to 0.46

0.37 to 0.43

0.39 to 0.41

0.40 to 0.42

.

5 points

Question 8

A sample of 1,108 was used to estimate a proportion with 98% confidence. If , what was the amount of error?

0.040

0.025

0.035

0.028

.

5 points

Question 9

After computing a confidence interval, the user believes the results are meaningless because the width of the interval is too large. Which one of the following is the best recommendation?

Increase the level of confidence for the interval.

Decrease the sample size.

Increase the sample size.

Reduce the population variance.

.

5 points

Question 10

As the confidence level decreases, the width of the confidence interval _______________.

Stays the same

Decreases

Increases

.

5 points

Question 11

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 _________ e-mail messages.

323

12

457

14

100

.

5 points

Question 12

Given n = 12, s2 = 44.90, and that the population is normally distributed, the 99% confidence interval for the population variance is _________ .

19.0391 ? ? 2 ? 175.2888

23.0881 ? ? 2 ? 122.3495

25.6253 ? ? 2 ? 103.0993

18.4588 ? ? 2 ? 189.7279

14.2929 ? ? 2 ? 139.2989

.

5 points

Question 13

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 _________ .

16.25 to 33.75

24.30 to 25.71

17.95 to 32.05

24.12 to 25.88

24.45 to 27.32

.

5 points

Question 14

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 __________ .

66.78 to 83.23

72.72 to 77.28

72.53 to 77.47

66.09 to 83.91

73.34 to 76.25

.

5 points

Question 15

The Academy of Orthopedic Surgeons states that 80% of women wear shoes that are too small for their feet. A researcher wants to be 98% confident that this proportion is within 3% of the true proportion. How large a sample is necessary?

966

683

1183

484

.

5 points

Question 16

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.

[63.19 76.21]

[62.49 76.91]

[69.65 69.75]

[69.47 69.93]

[69.44 69.96]

.

5 points

Question 17

The coffee/soup machine at the local bus station is supposed to fill cups with 6 ounces of soup. Ten cups of soup are brought with results of a mean of 5.93 ounces and a standard deviation of 0.13 ounces. Construct a 99% confidence interval for the true machine-fill amount. Carry your answer to 3 decimal places.

[5.888 5.972]

[5.814 6.046]

[5.716 6.144]

[5.824 6.036]

[5.796 6.064]

.

5 points

Question 18

The mean weight of trucks traveling on a particular section of I-475 is not known. A state highway inspector needs an estimate of the mean. He selects a random sample of 49 trucks passing the weighing station and finds the mean weight is 15.8 tons. The population standard deviation is 3.8 tons. What is the 95 percent interval for the population mean?

14.7 and 16.9

13.2 and 17.6

10.0 and 20.0

16.1 and 18.1

.

5 points

Question 19

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 _________ .

1.76 to 2.66

2.01 to 2.41

2.08 to 2.34

1.93 to 2.49

2.49 to 2.67

.

5 points

Question 20

When the level of confidence decreases, the margin of error

stays the same

becomes smaller

becomes larger

becomes smaller or larger, depending on the sample size

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