Question 1

When determining the sample size, if the value found is not an integer initially, you should ________ choose the next highest integer value.

Accepted Answer

A)  always 
B)  sometimes 
C)  never 
A)  always 
B)  sometimes 
C)  never

Question 2

A manufacturer of NFL regulation footballs uses a machine to inflate its new balls to a pressure of 13.5 pounds (σ = .1). When the machine is properly calibrated, the mean inflation pressure is 13.5 pounds, but uncontrollable factors can cause the pressure of individual footballs to vary. For quality control purposes, the manufacturer wishes to estimate the mean inflation pressure to within .025 pounds of its true value with 99 percent confidence. What sample size should be used?

Accepted Answer

A)  677 
B)  107 
C)  35 
D)  27 
E)  11 
A)  677 
B)  107 
C)  35 
D)  27 
E)  11

Question 3

The state agriculture department tested 203 fuel samples across the state in 2009 for accuracy of the reported octane level. For premium grade, 14 out of 105 samples failed. How many samples would be needed to create a 99 percent confidence interval that is within .02 of the true proportion of premium-grade fuel-quality failures?

Accepted Answer

A)  4148 
B)  2838 
C)  1913 
D)  744 
E)  54 
A)  4148 
B)  2838 
C)  1913 
D)  744 
E)  54

Question 4

On a standard IQ test, the standard deviation is 15. How many random IQ scores must be obtained if we want to find the true population mean (with an allowable error of .5) and we want 97 percent confidence in the results?

Accepted Answer

A)  4,239 
B)  283 
C)  212 
D)  131 
E)  66 
A)  4,239 
B)  283 
C)  212 
D)  131 
E)  66

Question 5

A sample of 2,000 people yielded   = .52. Calculate a 90 percent confidence interval for p.

Accepted Answer

A)  [.506, .534] 
B)  [.468, .572] 
C)  [.511, .529] 
D)  [.502, .538] 
A)  [.506, .534] 
B)  [.468, .572] 
C)  [.511, .529] 
D)  [.502, .538]

Question 6

A tolerance interval is always longer than a corresponding confidence interval.

Accepted Answer

A) True 
 B)False

Question 7

When solving for the sample size needed to compute a 95 percent confidence interval for a population proportion p, having a given error bound E, we choose a value of   that

Accepted Answer

A)  makes   (1 −
  ) as small as reasonably possible. 
B)  makes   (1 −
  ) as large as reasonably possible. 
C)  makes   (1 −
  ) as close to .5 as reasonably possible. 
D)  makes   (1 −
  ) as close to .25 as reasonably possible. 
E)  makes   (1 −
  ) as large as reasonably possible and makes
  (1 −
  ) as close to .25 as reasonably possible. 
A)  makes   (1 −
  ) as small as reasonably possible. 
B)  makes   (1 −
  ) as large as reasonably possible. 
C)  makes   (1 −
  ) as close to .5 as reasonably possible. 
D)  makes   (1 −
  ) as close to .25 as reasonably possible. 
E)  makes   (1 −
  ) as large as reasonably possible and makes
  (1 −
  ) as close to .25 as reasonably possible.

Question 8

An insurance analyst working for a car insurance company would like to determine the proportion of accident claims covered by the company. A random sample of 200 claims shows that the insurance company covered 80 accident claims and did not cover 120 claims. Construct a 90 percent confidence interval estimate of the true proportion of claims covered by the insurance company.

Accepted Answer

A)  [.356, .444] 
B)  [.360, .440] 
C)  [.372, .428] 
D)  [.343, .457] 
A)  [.356, .444] 
B)  [.360, .440] 
C)  [.372, .428] 
D)  [.343, .457]

Question 9

In a manufacturing process, a random sample of 9 manufactured bolts has a mean length of 3 inches with a variance of .09 and is normally distributed. What is the 90 percent confidence interval for the true mean length of the manufactured bolt?

Accepted Answer

A)  2.8355 to 3.1645 
B)  2.5065 to 3.4935 
C)  2.4420 to 3.5580 
D)  2.8140 to 3.1860 
E)  2.9442 to 3.0558 
A)  2.8355 to 3.1645 
B)  2.5065 to 3.4935 
C)  2.4420 to 3.5580 
D)  2.8140 to 3.1860 
E)  2.9442 to 3.0558

Question 10

Health insurers and the federal government are both putting pressure on hospitals to shorten the average length of stay (LOS) of their patients. In 2003, the average LOS for non-heart patients was 4.6 days. A random sample of 20 hospitals in one state had a mean LOS for non-heart patients in 2008 of 3.8 days and a standard deviation of 1.2 days and is normally distributed. Calculate a 95 percent confidence interval for the population mean LOS for non-heart patients in these hospitals in 2008.

Accepted Answer

A)  [3.24, 4.36] 
B)  [3.67, 3.93] 
C)  [3.34, 4.26] 
D)  [3.38, 4.22] 
E)  [3.27, 4.33] 
A)  [3.24, 4.36] 
B)  [3.67, 3.93] 
C)  [3.34, 4.26] 
D)  [3.38, 4.22] 
E)  [3.27, 4.33]

Question 11

A random sample of size 30 from a normal population yields   = 32.8 with a population standard deviation of 4.51. Construct a 95 percent confidence interval for μ.

Accepted Answer

A)  [23.96, 41.64] 
B)  [32.04, 33.56] 
C)  [31.45, 34.15] 
D)  [31.19, 34.41] 
A)  [23.96, 41.64] 
B)  [32.04, 33.56] 
C)  [31.45, 34.15] 
D)  [31.19, 34.41]

Question 12

In a manufacturing process a random sample of 9 manufactured bolts has a mean length of 3 inches with a standard deviation of .3 inches and is normally distributed. What is the 95 percent confidence interval for the true mean length of the manufactured bolt?

Accepted Answer

A)  2.804 to 3.196 
B)  2.308 to 3.692 
C)  2.769 to 3.231 
D)  2.412 to 3.588 
E)  2.814 to 3.186 
A)  2.804 to 3.196 
B)  2.308 to 3.692 
C)  2.769 to 3.231 
D)  2.412 to 3.588 
E)  2.814 to 3.186

Question 13

An experiment was conducted to determine the effectiveness of a method designed to remove oil wastes found in soil. Three contaminated soil samples were treated. After 95 days, the percentage of contamination removed from each soil sample was measured, with a mean of 49.3 percent and a standard deviation of 1.5 percent. If we wished to narrow the boundary around μ for a 98 percent confidence interval to within .5 percent, how many soil samples should be in our experiment?

Accepted Answer

A)  437 
B)  33 
C)  9 
D)  6 
E)  3 
A)  437 
B)  33 
C)  9 
D)  6 
E)  3

Question 14

The customer service manager for the XYZ Fastener Manufacturing Company examined 60 invoices and found 9 that contained errors. Find a 98 percent confidence interval for the proportion of invoices with errors.

Accepted Answer

A)  [.147, .153] 
B)  [.080, .220] 
C)  [.043, .257] 
D)  [.112, .188] 
A)  [.147, .153] 
B)  [.080, .220] 
C)  [.043, .257] 
D)  [.112, .188]

Question 15

A confidence interval for the population mean is an interval constructed around the ________.

Accepted Answer

A)  sample mean 
B)  population mean 
C)  z test statistic 
D)  t test statistic 
A)  sample mean 
B)  population mean 
C)  z test statistic 
D)  t test statistic

Question 16

Unoccupied seats on flights cause airlines to lose revenue. Suppose a large airline wants to estimate its average number of unoccupied seats per flight over the past year. Two hundred and twenty-five flight records are randomly selected and the number of unoccupied seats is noted, with a sample mean of 11.6 seats and a population standard deviation of 4.1 seats. How many flights should we select if we wish to estimate μ to within 5 seats and be 95 percent confident?

Accepted Answer

A)  44 
B)  3 
C)  2 
D)  110 
E)  6 
A)  44 
B)  3 
C)  2 
D)  110 
E)  6

Question 17

As the stated confidence level decreases, the width of the confidence interval ________.

Accepted Answer

A)  stays the same 
B)  decreases 
C)  increases 
A)  stays the same 
B)  decreases 
C)  increases

Question 18

An experiment was conducted to determine the effectiveness of a method designed to remove oil wastes found in soil. Three contaminated soil samples were treated. After 95 days, the percentage of contamination removed from each soil sample was measured, with a mean of 49.3 percent and a standard deviation of 1.5 percent. Estimate the mean percentage of contamination removed at a 98 percent confidence level.

Accepted Answer

A)  [48.36, 50.24] 
B)  [43.27, 55.33] 
C)  [47.29, 51.31] 
D)  [47.88, 50.72] 
E)  [46.47, 52.13] 
A)  [48.36, 50.24] 
B)  [43.27, 55.33] 
C)  [47.29, 51.31] 
D)  [47.88, 50.72] 
E)  [46.47, 52.13]

Question 19

There is an average of 22.455 employees at 22 office furniture dealers in a major metropolitan area, with a standard deviation of 18.52. Construct a 99 percent confidence interval for the true mean number of full-time employees at office furniture dealers.

Accepted Answer

A)  [11.014, 33.896] 
B)  [11.275, 33.635] 
C)  [12.284, 32.626] 
D)  [12.513, 32.397] 
E)  [20.072, 24.838] 
A)  [11.014, 33.896] 
B)  [11.275, 33.635] 
C)  [12.284, 32.626] 
D)  [12.513, 32.397] 
E)  [20.072, 24.838]

Question 20

A sample of 2,000 people yielded   = .52. Calculate a 95 percent confidence interval for p.

Accepted Answer

A)  [.509, .531] 
B)  [.494, .546] 
C)  [.498, .542] 
D)  [.502, .538] 
A)  [.509, .531] 
B)  [.494, .546] 
C)  [.498, .542] 
D)  [.502, .538]

When determining the sample size, if the value found is not an integer initially, you should ________ choose the next highest integer value.

On a standard IQ test, the standard deviation is 15. How many random IQ scores must be obtained if we want to find the true population mean (with an allowable error of .5) and we want 97 percent confidence in the results?

A sample of 2,000 people yielded = .52. Calculate a 90 percent confidence interval for p.

A tolerance interval is always longer than a corresponding confidence interval.

When solving for the sample size needed to compute a 95 percent confidence interval for a population proportion p, having a given error bound E, we choose a value of that

In a manufacturing process, a random sample of 9 manufactured bolts has a mean length of 3 inches with a variance of .09 and is normally distributed. What is the 90 percent confidence interval for the true mean length of the manufactured bolt?

A random sample of size 30 from a normal population yields = 32.8 with a population standard deviation of 4.51. Construct a 95 percent confidence interval for μ.

In a manufacturing process a random sample of 9 manufactured bolts has a mean length of 3 inches with a standard deviation of .3 inches and is normally distributed. What is the 95 percent confidence interval for the true mean length of the manufactured bolt?

The customer service manager for the XYZ Fastener Manufacturing Company examined 60 invoices and found 9 that contained errors. Find a 98 percent confidence interval for the proportion of invoices with errors.

A confidence interval for the population mean is an interval constructed around the ________.

As the stated confidence level decreases, the width of the confidence interval ________.

There is an average of 22.455 employees at 22 office furniture dealers in a major metropolitan area, with a standard deviation of 18.52. Construct a 99 percent confidence interval for the true mean number of full-time employees at office furniture dealers.

A sample of 2,000 people yielded = .52. Calculate a 95 percent confidence interval for p.

An Introduction to Business Statistics and Analytics

Descriptive Statistics and Analytics: Tabular and Graphical Methods

Descriptive Statistics and Analytics: Numerical Methods

Probability and Probability Models

Predictive Analytics I: Trees, K-Nearest Neighbors, Naive Bayes,

Discrete Random Variables

Continuous Random Variables

Sampling Distributions

Hypothesis Testing

Statistical Inferences Based on Two Samples

Experimental Design and Analysis of Variance

Chi-Square Tests

Simple Linear Regression Analysis

Multiple Regression and Model Building

Predictive Analytics Ii: Logistic Regression, Discriminate Analysis,

Time Series Forecasting and Index Numbers

Nonparametric Methods

Decision Theory

Filters

Exam 9: Confidence Intervals

When determining the sample size, if the value found is not an integer initially, you should ________ choose the next highest integer value.

On a standard IQ test, the standard deviation is 15. How many random IQ scores must be obtained if we want to find the true population mean (with an allowable error of .5) and we want 97 percent confidence in the results?

A sample of 2,000 people yielded = .52. Calculate a 90 percent confidence interval for p.

A tolerance interval is always longer than a corresponding confidence interval.

When solving for the sample size needed to compute a 95 percent confidence interval for a population proportion p, having a given error bound E, we choose a value of that

In a manufacturing process, a random sample of 9 manufactured bolts has a mean length of 3 inches with a variance of .09 and is normally distributed. What is the 90 percent confidence interval for the true mean length of the manufactured bolt?

A random sample of size 30 from a normal population yields = 32.8 with a population standard deviation of 4.51. Construct a 95 percent confidence interval for μ.

In a manufacturing process a random sample of 9 manufactured bolts has a mean length of 3 inches with a standard deviation of .3 inches and is normally distributed. What is the 95 percent confidence interval for the true mean length of the manufactured bolt?

The customer service manager for the XYZ Fastener Manufacturing Company examined 60 invoices and found 9 that contained errors. Find a 98 percent confidence interval for the proportion of invoices with errors.

A confidence interval for the population mean is an interval constructed around the ________.

As the stated confidence level decreases, the width of the confidence interval ________.

There is an average of 22.455 employees at 22 office furniture dealers in a major metropolitan area, with a standard deviation of 18.52. Construct a 99 percent confidence interval for the true mean number of full-time employees at office furniture dealers.

A sample of 2,000 people yielded = .52. Calculate a 95 percent confidence interval for p.

An Introduction to Business Statistics and Analytics

Descriptive Statistics and Analytics: Tabular and Graphical Methods

Descriptive Statistics and Analytics: Numerical Methods

Probability and Probability Models

Predictive Analytics I: Trees, K-Nearest Neighbors, Naive Bayes,

Discrete Random Variables

Continuous Random Variables

Sampling Distributions

Hypothesis Testing

Statistical Inferences Based on Two Samples

Experimental Design and Analysis of Variance

Chi-Square Tests

Simple Linear Regression Analysis

Multiple Regression and Model Building

Predictive Analytics Ii: Logistic Regression, Discriminate Analysis,

Time Series Forecasting and Index Numbers

Nonparametric Methods

Decision Theory

Filters