A+ Answers



Question 1 

Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker. 

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values. 

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not. 

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 today‚Äôs sample contains 14 defectives. 

Determine a 95% confidence interval for the proportion defective for the process today. 

Place your LOWER limit, rounded to 3 decimal places, in the first blank. For example, 0.123 would be a legitimate answer. 

Place your UPPER limit, rounded to 3 decimal places, in the second blank. For example, 0.345 would be a legitimate entry. 

Question 2 

Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker. 

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values. 

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not. 

If a sample has 20 observations and a 95% confidence estimate for  is needed, the appropriate value of the t-multiple required is. Place your answer, rounded to 3 decimal places, in the blank. For example, 4.567 would be a legitimate entry. 

Question 3 

Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker. 

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values. 

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not. 

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 

Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker. 

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values. 

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not. 

The manufacturer of a new compact car claims the miles per gallon (mpg) for the gasoline consumption is mound-shaped and symmetric with a mean of 25.9 mpg and a standard deviation of 9.5 mpg. If 30 such cars are tested, what is the probability the average mpg achieved by these 30 cars will be greater than 28? 

Answer:   Round your answer to 4 decimal places as necessary.  For example, 0.1357 would be a legitimate entry. 

Question 5 

Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker. 

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values. 

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not. 

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 

Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker. 

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values. 

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not. 

A marketing research consultant hired by Coca-Cola is interested in determining the proportion of customers who favor Coke over other soft drinks. A random sample of 400 consumers was selected from the market under investigation and showed that 53% favored Coca-Cola over other brands. 

Compute a 95% confidence interval for the true proportion of people who favor Coke. Place your LOWER limit, rounded to 3 decimal places, in the first blank. For example, .345 would be a legitimate entry. Place your UPPER limit in the second blank. For example, .456 would be a legitimate entry. 

Question 7 

Accepted characters: numbers, decimal point markers (period or comma), sign indicators (-), spaces (e.g., as thousands separator, 5 000), “E” or “e” (used in scientific notation). NOTE: For scientific notation, a period MUST be used as the decimal point marker. 

Complex numbers should be in the form (a + bi) where “a” and “b” need to have explicitly stated values. 

For example: {1+1i} is valid whereas {1+i} is not. {0+9i} is valid whereas {9i} is not. 

After calculating the sample size needed to estimate a population proportion to within 0.05, you have been told that the maximum allowable error (E) must be reduced to just 0.025. If the original calculation led to a sample size of 1000, the sample size will now have to be. Place your answer, as a whole number in the blank. For example, 2345 would be a legitimate entry. 

Question 8 

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

A.decreases 

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

C.stays the same 

D.increases 

Question 9 

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 

Question 10 

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 

Question 11 

From a sample of 500 items, 30 were found to be defective. The point estimate of the population proportion defective will be:

A.16.667 

B.0.60 

C.30 

D..06 

Question 12 

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 

Question 13 

A sample of 23 European countries found that the variance of life expectancy was 7.3 years. What is the 95% confidence interval estimate for the variance of life expectancy in Europe?

A.27.2 < < 118.3 

B.5.6 < < 10.3 

C.4.4 < < 14.6 

D.28.9 < < 115.0 

Question 14 

If you are constructing a confidence interval for a single mean, the confidence interval will___________ with an increase in the sample size.

A.increase or decrease, depending on the sample data 

B.decrease 

C.stay the same 

D.increase 

Question 15 

The t- distribution for developing a confidence interval for a mean has _____ degrees of freedom.

A.n – 2 

B.n + 1 

C.n – 1 

D.n 

Question 16 

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.31 

B.39 

C.50 

D.166 

Question 17 

A recent study of 750 Internet users in Europe found that 35% of Internet users were women. What is the 95% confidence interval estimate for the true proportion of women in Europe who use the Internet?

A.0.321 < p < 0.379  

B.0.316 < p < 0.384  

C.0.309 < p < 0.391  

D.0.305 < p < 0.395 

Question 18 In constructing a confidence interval estimate for a population mean, when we replace  with the sample standard deviation (s), we introduce a new source of variability and the sampling distribution we use is:

A.chi-square distribution 

B.the normal distribution 

C.t -distribution 

D.F- distribution 

Part 3 of 3 – 

Question 19 

A 90% confidence interval estimate for a population mean is determined to be 72.8 to 79.6. If the confidence level is reduced to 80%, the confidence interval becomes narrower.

True

False

Question 20 

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