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Question 1 of 20 1.0 Points

You are trying to estimate the average amount a family spends on food during a year. In the past, the standard deviation of the amount a family has spent on food during a year has been $1200. If you want to be 99% sure that you have estimated average family food expenditures within $60, how many families do you need to survey? Place your answer, a whole number, in the blank . For example, 1234 would be a legitimate entry.

Question 2 of 20 1.0 Points

The percent defective for parts produced by a manufacturing process is targeted at 4%. The process is monitored daily by taking samples of sizes n = 160 units. Suppose that todays sample contains 14 defectives.

How many units would have to be sampled to be 95% confident that you can estimate the fraction of defective parts within 2% (using the information from todays sample–that is using the result that )?

Place your answer, as a whole number, in the blank. For example 567 would be a legitimate entry.

Question 3 of 20 1.0 Points

The personnel department of a large corporation wants to estimate the family dental expenses of its employees to determine the feasibility of providing a dental insurance plan. A random sample of 12 employees reveals the following family dental expenses (in dollars): 115, 370, 250, 593, 540, 225, 177, 425, 318, 182, 275, and 228.

Construct a 99% confidence interval estimate for the standard deviation of family dental expenses for all employees of this corporation.

Place your LOWER limit, in dollars rounded to 1 decimal place, in the first blank. Do not use a dollar sign, a comma, or any other stray mark. For example, 98.4 would be a legitimate entry.

Place your UPPER limit, in dollars rounded to 1 decimal place, in the second blank. Do not use a dollar sign, a comma, or any other stray mark. For example, 567.8 would be a legitimate entry.

Question 4 of 20 1.0 Points

You are told that a random sample of 150 people from Iowa has been given cholesterol tests, and 60 of these people had levels over the safe count of 200. Construct a 95% confidence interval for the population proportion of people in Iowa with cholesterol levels over 200. Place your LOWER limit, rounded to 3 decimal places, in the first blank . For example, .678 would be a legitimate entry. Place your UPPER limit, rounded to 3 decimal places, in the second blank . For example, .789 would be a legitimate entry.

Question 5 of 20 1.0 Points

A lawyer researched the average number of years served by 45 different justices on the Supreme Court. The average number of years served was 13.8 years with a standard deviation of 7.3 years. What is the 95% confidence interval estimate for the average number of years served by all Supreme Court justices? Place your limits, rounded to 1 decimal place, in the blanks. Place you lower limit in the first blank. Place your upper limit in the second blank. When entering your answer do not use any labels or symbols. Simply provide the numerical value. For example, 12.3 would be a legitimate entry.

Question 6 of 20 1.0 Points

The personnel department of a large corporation wants to estimate the family dental expenses of its employees to determine the feasibility of providing a dental insurance plan. A random sample of 12 employees reveals the following family dental expenses (in dollars): 115, 370, 250, 593, 540, 225, 177, 425, 318, 182, 275, and 228.

Construct a 90% confidence interval estimate for the standard deviation of family dental expenses for all employees of this corporation.

Place your LOWER limit, in dollars rounded to 1 decimal place, in the first blank. Do not use a dollar sign, a comma, or any other stray mark. For example, 123.4 would be a legitimate entry.

Place your UPPER limit, in dollars rounded to 1 decimal place, in the second blank. Do not use a dollar sign, a comma, or any other stray mark. For example, 567.8 would be a legitimate entry.

Question 7 of 20 1.0 Points

Senior management of a consulting services firm is concerned about a growing decline in the firms weekly number of billable hours. The firm expects each professional employee to spend at least 40 hours per week on work. In an effort to understand this problem better, management would like to estimate the standard deviation of the number of hours their employees spend on work-related activities in a typical week. Rather than reviewing the records of all the firms full-time employees, the management randomly selected a sample of size 51 from the available frame. The sample mean and sample standard deviations were 48.5 and 7.5 hours, respectively.

Construct a 95% confidence interval for the standard deviation of the number of hours this firms employees spend on work-related activities in a typical week.

Place your LOWER limit, in hours, rounded to 1 decimal place, in the first blank. For example, 6.7 would be a legitimate entry.

Place your UPPER limit, in hours, rounded to 1 decimal place, in the second blank. For example, 12.3 would be a legitimate entry.

Part 2 of 3 –

Question 8 of 20 1.0 Points

At a large department store, the average number of years of employment for a cashier is 5.7 with a standard deviation of 1.8 years. If the number of years of employment at this department store is normally distributed, what is the probability that a cashier selected at random has worked at the store for over 10 years?

A. 0.4916

B. 0.9916

C. 0.0084

D. 0.0054

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Question 9 of 20 1.0 Points

If you increase the confidence level, the confidence interval ____________.

A. may increase or decrease, depending on the sample data

B. stays the same

C. increases

D. decreases

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Question 10 of 20 1.0 Points

A sample of 25 different payroll departments found that the employees worked an average of 310.3 days a year with a standard deviation of 23.8 days. What is the 90% confidence interval for the average days worked by employees in all payroll departments?

A. 301.0 < < 319.6
B. 298.0 < < 322.6
C. 302.2 < < 318.4
D. 314.1 < < 316.8
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Question 11 of 20 1.0 Points
In a study of elephants a researcher wishes to determine the average weight of a certain subspecies of elephants. From previous studies, the standard deviation of the weights of elephants in this subspecies is known to be 1500 pounds. How many elephants does the researcher need to weigh so that he can be 80% confident that the average weight of elephants in his sample is within 350 pounds of the true average weight for this subspecies?
A. 166
B. 50
C. 31
D. 39
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Question 12 of 20 1.0 Points
The t- distribution for developing a confidence interval for a mean has _____ degrees of freedom.
A. n
B. n - 2
C. n - 1
D. n + 1
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Question 13 of 20 1.0 Points
A researcher wishes to know, with 98% confidence, the percentage of women who wear shoes that are too small for their feet. A previous study conducted by the Academy of Orthopedic Surgeons found that 80% of women wear shoes that are too small for their feet. If the researcher wants her estimate to be within 3% of the true proportion, how large a sample is necessary?
A. 966
B. 683
C. 183
D. 484
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Question 14 of 20 1.0 Points
Confidence intervals are a function of which of the following three things?
A. The population, the sample, and the standard deviation
B. The sampling distribution, the confidence level, and the degrees of freedom
C. The data in the sample, the confidence level, and the sample size
D. The sample, the variable of interest, and the degrees of freedom
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Question 15 of 20 1.0 Points
Which of the following will make a confidence interval narrower and more precise?
A. Smaller sample size and lower confidence level
B. Smaller sample size and higher confidence level
C. Larger sample size and lower confidence level
D. Larger sample size and higher confidence level
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Question 16 of 20 1.0 Points
Compute where t15 has a t-distribution with 15 degrees of freedom.
A. 0.96803
B. 0.93606
C. 0.03197
D. 0.7639
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Question 17 of 20 1.0 Points
A food snack manufacturer samples 15 bags of pretzels off the assembly line and weighed their contents. If the sample mean is 10.0 and the sample standard deviation is 0.15, find the 95% confidence interval estimate for the true mean.
A. (9.96, 10.04)
B. (9.68, 10.32)
C. (9.97, 10.80)
D. (9.92, 10.08)
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Question 18 of 20 1.0 Points
In order to be accepted into a top university, applicants must score within the top 5% on the SAT exam. Given that SAT test scores are normally distributed with a mean of 1000 and a standard deviation of 200, what is the lowest possible score a student needs to qualify for acceptance into the university?
A. 1330
B. 1400
C. 1250
D. 1100
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Part 3 of 3 -
Question 19 of 20 1.0 Points
The lower limit of the 95% confidence interval for the population proportion p, given that n = 300; and = 0.10 is 0.1339. True
False
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Question 20 of 20 1.0 Points
The upper limit of the 95% confidence interval for the population proportion p, given that n = 300; and = 0.10 is approximately 0.1339. True
False

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