Deck 9: Statistical Inferences Based on Two Samples

Question 1

Consider a confidence interval for a population mean.As the standard deviation ________,sample sizes need to _____________ to achieve a specified margin of error.

A)increases,increase
B)decreases,increase
C)increases,decrease
D)increases,remain the same
E)decreases,remain the same

Answer 1

A

Question 2

When the level of confidence and sample size remain the same,a confidence interval for a population proportion p will be narrower when $\hat { p } ( 1 - \hat { p } )$
is larger than when $\hat { p } ( 1 - \hat { p } )$
is smaller.

Answer 2

False

Question 3

Consider a normally distributed population.Which two of the following actions will result in the greatest increase in the width of a confidence interval for the mean?
(i)increasing the confidence level
(ii)decreasing the confidence level
(iii)increasing the sample size
(iv)decreasing the sample size
(v)decreasing the standard deviation

A)(i)and (iii)
B)(ii)and (iv)
C)(ii)and (iii)
D)(i)and (v)
E)(i)and (iv)

Answer 3

E

Question 4

An injector molder produces plastic pens.The process is designed to produce pens with a mean weight of 0.250 grams.To investigate whether the injection molder is operating satisfactorily,40 pens were randomly sample with a mean of 0.2525g.The population standard deviation is believed to be approximately 0.0022g.Find a 99% confidence interval for the population mean.

A)[.2514;2536]
B)[.2516;534]
C)[.2517;2533]
D)[.2518;2532]
E)[.2521;2529]

Question 5

Consider a normally distributed population with standard deviation 36.If we wish to estimate the population mean to within 10 units with 90% confidence,what is the required sample size?

A)36
B)35
C)6
D)59
E)5922

Question 6

Suppose we are interested in the population mean of a normally distributed population with unknown standard deviation.If we take a sample of 12 observations from this population,the confidence interval for the population mean is computed based on the t distribution.

Question 7

If we wish to estimate a population proportion to within 5% with 95% confidence,the required sample size is 385.

Question 8

When the level of confidence and sample proportion $\hat { p }$
remain the same,a confidence interval for a population proportion p based on a sample of n = 100 will be wider than a confidence interval for p based on a sample of n = 400.

Question 9

We wish to compute a confidence interval for a population mean.Suppose we are determining the sample size n needed to achieve a desired margin of error for this interval.If we compute the value of n to be 79.2,we would choose to sample 79 observations.

Question 10

A 95% confidence interval for a population proportion is computed to be [0.14,0.36].This means that each time we take a sample from this population,the sample proportion has a 95% chance of being between 0.14 and 0.36.

Question 11

When the population is normally distributed and the population standard deviation $\sigma$
is unknown,then for any sample size n,the confidence interval for $\mu$
is based on the z distribution.

Question 12

When the level of confidence and standard deviation remain the same,a confidence interval for a population mean based on a sample of n = 100 will be narrower than a confidence interval for a population mean based on a sample of n = 50.

Question 13

All other things being constant,the margin of error for a confidence interval for a population mean increases as the sample size decreases.

Question 14

It is appropriate to compute a confidence interval for a population proportion p if $n \hat { p }$
and $n ( 1 - \hat { p } )$
are both at least 5.

Question 15

Consider a normally distribution population with known variance.The width of a 99% confidence interval for the population mean will be _______ the width of a 95% confidence interval for the population mean:

A)less than
B)equal to
C)greater than
D)4% larger than
E)4% smaller than

Question 16

Assuming the same confidence level $1 - \alpha$
,as the sample size increases,the value of $t _ { \alpha / 2 }$
approaches the value of $z _ { \alpha / 2 }$
.

Question 17

For a fixed sample size and standard deviation,the width of a confidence interval for a population mean $\mu$
will increase as the level of confidence decreases.

Question 18

When constructing a confidence interval for a sample proportion,the t distribution is appropriate if the sample size is small.

Question 19

When constructing a confidence interval for a population mean,if the population is normally distributed with unknown standard deviation and the sample size is 10,then the distribution of $\bar { x }$
Is based on _____ distribution.

A)z
B)t
C)F
D)chi-square
E)binomial

Question 20

When computed based on the same sample,the 99% confidence interval for a population mean $\mu$
will be narrower than the 95% confidence interval for $\mu$
.

Question 21

A company is interested in estimating $$\mu$$ , the mean number of days of sick leave taken by its employees. The firm's statistician randomly selects 100 personnel files and notes the number of sick days taken by each employee. The sample mean is 12.2 days. From historical records, the population standard deviation is about 10 days.

-How many personnel files would the director have to select in order to estimate $\mu$
To within 2 days with 99% confidence?

A)2
B)13
C)136
D)165
E)166

Question 22

When constructing a confidence interval for a population mean,if the population is normally distributed with known standard deviation and the sample size is n = 5,then the distribution of $\bar { x }$
Is based on _____ distribution.

A)z
B)t
C)F
D)chi-square
E)binomial

Question 23

Consider a normally distributed population with unknown standard deviation.When computing a confidence interval for the population mean,the values $t _ { \alpha / 2 }$
And $z _ { \alpha / 2 }$
Will be close in value when

A)the sample size is small.
B)the sample size is large.
C)the sample mean is small.
D)the sample mean is large.
E)the sample standard deviation is small.

Question 24

When a confidence interval for a population proportion is constructed for a sample size of 30 and the value of $\hat { p }$
Is 0.4,the confidence interval is based on the ____ distribution.

A)z
B)t
C)F
D)exponential
E)Poisson

Question 25

When the level of confidence and sample proportion $\hat { p }$
Remain the same,a confidence interval for a population proportion p based on a sample of n = 100 will be ______________ a confidence interval for p based on a sample of n = 400.

A)wider than
B)narrower than
C)equal to

Question 26

A random sample of 1000 customers at a fast food restaurant had their service time recorded.Based on this sample,a 95% confidence interval for the average service time,in minutes,at the restaurant is computed to be [4.1,7.5].How would you interpret this interval?

A)95% of all customers have a service time between 4.1 minutes and 7.5 minutes.
B)We are 95% confident that the population mean service time is between 4.1 minutes and 7.5 minutes.
C)We are 95% confident that the sample mean service time is between 4.1 minutes and 7.5 minutes.
D)950 of the 1000 customers in the sample will have a service time is between 4.1 minutes and 7.5 minutes.
E)If we select one new customer at random,the probability their service time will be between 4.1 minutes and 7.5 minutes is 0.95.

Question 27

In a manufacturing process a random sample of 36 bolts manufactured has a mean length of 3cm with a standard deviation of 0.3cm.Assuming bolt length is normally distributed,what is the 99% confidence interval for the true mean length of the bolt?

A)2.902 to 3.098
B)2.884 to 3.117
C)2.864 to 3.136
D)2.228 to 3.772
E)2.902 to 3.772

Question 28

A Research and Development Laboratory researcher for a paint company is measuring the level of a certain chemical contained in a certain type of paint.If the paint contains too much of this chemical,the quality of the paint will be compromised.How many cans of paint should the sample contain if the researcher wants to be 95% certain of being within 1% of the true proportion of this chemical?

A)9604
B)1107
C)26
D)645
E)5936

Question 29

You wish to compute a confidence interval for $\mu _ { 1 } - \mu _ { 2 }$
For two normally distributed populations.Independent random samples of are taken from each population.The relevant sample statistics are n₁ = 10,n₂ = 8,s₁ = 5,and s₂= 7.If we assume the population variances are equal,give a pooled estimate of this common variance.

A)28.2
B)29.7
C)41.8
D)35.5
E)42.3

Question 30

A machine has been designed to make nails which are 8cm long with a standard deviation of 0.15cm.A sample of 48 nails is selected periodically to assess if the length is too variable from the standard of 8cm.From the sample of 48 nails,the mean is found to be 7.983cm.Assume the lengths are normally distributed and the standard deviation is known to be 0.15cm.Compute the 95% confidence interval for the population mean nail length.

A)[7.947,8.019]
B)[7.941,8.025]
C)[7.933,8.033]
D)[7.955,8.011]
E)[7.916,8.050]

Question 31

When the sample size and the sample proportion $\hat { p }$
Remain the same,a 90% confidence interval for a population proportion p will be ____________ the 99% confidence interval for p.

A)wider than
B)narrower than
C)equal to

Question 32

The internal auditing staff of a local manufacturing company performs a sample audit each quarter to estimate the proportion of accounts that are delinquent (more than 90 days overdue).For this quarter,the auditing staff randomly selected 400 customer accounts and found that 80 of these accounts were delinquent.What is the 95% confidence interval for the proportion of all delinquent customer accounts at this manufacturing company?

A)1608 to .2392
B)1992 to .2008
C)1671 to .2329
D)1485 to .2515
E)1714 to .2286

Question 33

Consider a normally distribution population with known variance.A 95% confidence interval is computed based on sample of 25 observations.If we take a new sample of 100 observations and compute a second 95% confidence interval based on the new sample,we know that the width of the second confidence interval will be exactly ____ times the width of the first confidence interval.

A)2
B)0.5
C)4
D)0.25
E)We cannot answer this question without knowing the sample means from both samples.

Question 34

In a manufacturing process a random sample of 9 bolts manufactured has a mean length of 3cm with a variance of 0.09.Assuming bolt length is normally distributed,what is the 90% confidence interval for the true mean length of the bolt?

A)2.8355 to 3.1645
B)2.5065 to 3.4935
C)2.4420 to 3.5580
D)2.8140 to 3.8160
E)2.9442 to 3.0558

Question 35

Consider a normally distributed population.The width of a confidence interval for the population mean will be

A)smaller for a 98% confidence than for 90% confidence.
B)larger for a sample size of 64 than for a sample size of 36.
C)larger for a 99% confidence than for 95% confidence.
D)smaller for sample size of 25 than for a sample size of 36.
E)larger for a standard deviation of 25 units than for a standard deviation of 50 units.

Question 36

A company is interested in estimating $$\mu$$ , the mean number of days of sick leave taken by its employees. The firm's statistician randomly selects 100 personnel files and notes the number of sick days taken by each employee. The sample mean is 12.2 days. From historical records, the population standard deviation is about 10 days.

-A 93% confidence interval for $\mu$
,the mean number of days of sick leave would be _____.

A)[10.725,13.675]
B)[10.390,14.010]
C)[12.019,12.381]
D)[12.053,12.348]
E)[11.735,12.665]

Question 37

A manager is interested in the amount of time employees spend each day playing video games at work.The manager takes a random sample of 18 employees who showed a mean time of 55 minutes per day with a standard deviation of 5 minutes.Assuming that these times follow a normal distribution,compute a 90% confidence interval for the average amount of time employees spend playing video games each day at work.

A)[52.39,57.61]
B)[52.95,57.05]
C)[52.82,57.18]
D)[53.34,56.66]
E)[52.46,57.54]

Question 38

Independent random samples of are taken from each of two normally distributed populations.The relevant sample statistics are n₁ = 10,n₂ = 8, $\bar { x } _ { 1 }$
= 50, $\bar { x } _ { 2 }$
= 42,s₁= 5,and s₂ = 7.If we assume the population variances are equal,give a 95% confidence for $\mu _ { 1 } - \mu _ { 2 }$
)

A)[2.01,13.99]
B)[1.08,14.91]
C)[3.51,12.49]
D)[2.56,13.44]
E)[4.62,11.38]

Question 39

You wish to compute a confidence interval for a population proportion p.For a constant confidence level and sample size,which of the following values of $\hat { p }$
Will result in the interval with the shortest width?

A)0.5
B)0.9
C)0.8
D)0.2
E)0.4

Question 40

In a manufacturing process a random sample of 9 bolts manufactured has a mean length of 3cm with a standard deviation of .3cm.Assuming bolt length is normally distributed,what is the 95% confidence interval for the true mean length of the bolt?

A)2.804 to 3.196
B)2.308 to 3.692
C)2.770 to 3.231
D)2.412 to 3.588
E)2.814 to 3.186

Question 41

A granola bar manufacturer states that their granola bars contain 28 grams of carbohydrates per bar.A sample of five granola bars is tested and a mean of 28.2g is obtained with a standard deviation of 2.7g.If carbohydrate content is normally distributed,the 95% confidence interval for the mean carbohydrate content of all such granola bars made by this company would be _____.

A)[26.16,30.24]
B)[20.70,35.70]
C)[24.85,31.55]
D)[26.70,29.70]
E)[25.83,30.57]

Question 42

A local company makes a candy that is supposed to weigh 1.00 gram.A random sample of 25 pieces of candy produces a mean of 0.996g with a standard deviation of 0.004g.If candy weight is normally distributed,how many pieces of candy must we sample if we want to be 99% confident that the sample mean is within 0.001g of the true mean?

A)126
B)124
C)107
D)12
E)6

Question 43

The provincial transportation department is studying traffic patterns on one of the busiest highways in the province.As part of the study,the department needs to estimate the average number of vehicles that pass an intersection each day to within 300 cars with 99% confidence.If the population standard deviation is 1,010 cars,how many days do they need to sample?

A)109
B)76
C)75
D)62
E)9

Question 44

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.A preliminary study of 10 flights reveals a sample standard deviation of 6.3 empty seats.How many flights should we select if we wish to estimate $\mu$
To within 1 seats and be 95% confident? Assume the number of empty seats can be approximated by a normal distribution.

A)130
B)65
C)204
D)17
E)12

Question 45

A psychologist is collecting data on the time it takes to learn a certain task.For 50 randomly selected adult subjects,the sample mean is 16.40 minutes and the sample standard deviation is 4.00 minutes.The 95% confidence interval for the mean time required by all adults to learn the task would be _____.

A)[8.56,24.24]
B)[15.47,17.33]
C)[16.24,16.56]
D)[15.26,17.54]
E)[17.12,48.48]

Question 46

Sandwiches sold at a local grocery store claim to have 6 grams of fat per sandwich.Ten sandwiches are brought with results of a mean of 5.93g of fat and a standard deviation of 0.13g.If fat content is normally distributed,the 99% confidence interval for the true fat content would be _____.

A)[5.888,5.972]
B)[5.814,6.046]
C)[5.716,6.144]
D)[5.824,6.036]
E)[5.796,6.064]

Question 47

A local company makes a candy that is supposed to weigh 1.00 gram.A random sample of 25 pieces of candy produces a mean of 0.996g with a standard deviation of 0.004g.If candy weight is normally distributed,the 98% confidence interval for the mean weight of all such candy would be _____.

A)[0.9645,1.0275]
B)[0.9956,0.9964]
C)[0.9860,1.0060]
D)[0.9940,0.9980]
E)[0.9942,0.9978]

Question 48

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.225 flight records are randomly selected and the number of unoccupied seats is noted with a sample mean of 11.6 seats and a standard deviation of 4.1 seats.A 90% confidence interval for $\mu$
,the mean number of unoccupied seats per flight during the past year would be _____.

A)[4.86,18.34]
B)[11.25,11.95]
C)[11.57,11.63]
D)[11.15,12.05]
E)[11.30,12.20]

Question 49

Health insurers and the federal government are both putting pressure on hospitals to shorten the average length of stay (LOS)of their patients.In 1996,the average LOS for non-heart patient was 4.6 days.A random sample of 20 hospitals had a mean LOS for non-heart patients in 2000 of 3.8 days and a standard deviation of 1.2 days.Assume LOS is normally distributed.How large a sample of hospitals would we need to be 99% confident that the sample mean is within 0.5 days of the population mean?

A)3
B)7
C)32
D)48
E)96

Question 50

At the end of 1990,1991,and 1992 the average prices of a share of stock in a money market portfolio were $34.83,$34.65 and $31.26 respectively.To investigate the average share price at the end of 1993,a random sample of 30 stocks was drawn and their closing prices on the last trading day of 1993 were observed with a mean of 33.583 and a standard deviation of 19.149.Assuming that stock prices are normally distributed,a 90% confidence interval would be _____.

A)[27.643,39.523]
B)[26.732,40.434]
C)[32.514,34.651]
D)[32.533,34.633]
E)[32.269,34.897]

Question 51

Research has been conducted that studies the role that the age of workers has in determining the hours per month spent on personal tasks.A sample of 1,686 adults were observed for one month.The data are: $\begin{array}{llll}&\text { AGE GROUP }\\&18-24&25-44&45-64\\\text { Mean } & 4.17 & 4.04 & 4.31 \\\text { Std Dev } & 0.75 & 0.81 & 0.82 \\\mathrm{~N} & 241 & 768 & 677\end{array}$
A 98% confidence interval for the mean hours spent on personal tasks would be _____.

A)[3.96,4.12]
B)[4.12,4.21]
C)[3.98,4.10]
D)[2.16,5.92]
E)[3.95,4.13]

Question 52

A sociologist develops a test designed to measure a person's attitudes about disabled people,and 16 randomly selected subjects are given the test.Their mean score is 71.2 with a standard deviation of 10.5.If the score is normally distributed,the 99% confidence interval for the mean score of all subjects would be _____.

A)[40.26,102.14]
B)[63.46,78.94]
C)[60.66,81.74]
D)[64.44,77.96]
E)[63.21,79.19]

Question 53

In a study of factors affecting job satisfaction,320 employed individuals were measured for an index of satisfaction and the sample mean was 28.8 and the sample standard deviation was 7.3.Following,the 98% confidence interval for the population mean would be _____.

A)[27.85,29.75]
B)[27.96,29.64]
C)[11.82,45.78]
D)[28.75,28.85]
E)[28.60,29.00]

Question 54

A market research company was interested in assessing how much money a single adult typically spent on groceries in one week.Participants were 772 single adults and the mean weekly grocery expenditure was found to be $69.70 with a standard deviation of $2.80.The 99% confidence interval for the mean weekly grocery expenditures for single adults would be _____.

A)[63.19,76.21]
B)[62.49,76.91]
C)[69.65,69.75]
D)[69.47,69.93]
E)[69.44,69.96]

Question 55

Health insurers and the federal government are both putting pressure on hospitals to shorten the average length of stay (LOS)of their patients.In 1996,the average LOS for non-heart patient was 4.6 days.A random sample of 20 hospitals had a mean LOS for non-heart patients in 2000 of 3.8 days and a standard deviation of 1.2 days.Assume LOS is normally distributed.A 95% confidence interval for the population mean LOS for non-heart patients in hospitals for 2000 would be _____.

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 56

A granola bar manufacturer states that their granola bars contain 28 grams of carbohydrates per bar.A sample of five granola bars is tested and a mean of 28.2g is obtained with a standard deviation of 2.7g.If carbohydrate content is normally distributed,how many granola bars should be tested to estimate the true mean grams of carbohydrates per bar to within 0.5g with 99% confidence?

A)25
B)124
C)194
D)618
E)619

Question 57

Sandwiches sold at a local grocery store claim to have 6 grams of fat per sandwich.Ten sandwiches are brought with results of a mean of 5.93g of fat and a standard deviation of 0.13g.If fat content is normally distributed,how large a sample of sandwiches would we need to be 95% confident that the sample mean is within 0.03g of the population mean?

A)97
B)96
C)73
D)62
E)10

Question 58

The provincial transportation department is studying traffic patterns on one of the busiest highways in the province.As part of the study,the department needs to estimate the average number of vehicles that pass an intersection each day.A random sample of 64 days gives us a sample mean of 14,205 cars.Historically,the population standard deviation has been approximately 1,010 cars.What is the 92% confidence interval estimate of $\mu$
,the mean number of cars passing the intersection?

A)[12,438,15,972]
B)[14,028,14,382]
C)[12,189,14,221]
D)[13,984,14,426]
E)[14,183,14,227]

Question 59

An auditor was hired to verify the accuracy of a company's new billing system.Thirty-five (35)invoices produced since the system was installed were sampled.The average error on the invoices was $1.00.Historically,the population standard deviation is around $124.00.A 97% confidence interval for the mean error per invoice would be _____.

A)[-268.08,270.08]
B)[-6.69,8.69]
C)[-44.48,46.48]
D)[-38.40,40.40]
E)[-9.17,11.66]

Question 60

In a random sample of 651 computer scientists who subscribed to a web-based daily news update,it was found that the average salary was $46,816 with a standard deviation of $12,557.A 91% confidence interval for the mean salary of computer scientists would be _____.

A)[$25,469 $68,163]
B)[$46,592 $47,040]
C)[$46,157 $47,475]
D)[$46,783 $46,849]
E)[$45,979 $47,653]

Question 61

In a poll of 1,004 adults,934 indicated that restaurants and bars should refuse service to patrons who have had too much to drink.The 90% confidence interval for the proportion of all adults who feel the same way would be _____.

A)[.078,.108]
B)[.914,.946]
C)[.920,.940]
D)[.917,.943]
E)[.910,.950]

Question 62

The Ministry of Agriculture tested 105 fuel samples for accuracy of the reported octane level.For premium grade,14 out of 105 samples failed (they didn't meet specifications).How many samples would be needed to create a 95% confidence interval that is within 0.02 of the true proportion of premium grade fuel-quality failures?

A)4148
B)1110
C)1913
D)744
E)54

Question 63

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% and a standard deviation of 1.5%.Assume the percentage of contamination is normally distributed.If we wished to narrow the boundary around μ for a 98% confidence interval to within 0.5%,how many soil samples should be in our experiment?

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

Question 64

The internal auditing staff of a local manufacturing company performs a sample audit each quarter to estimate the proportion of accounts that are current (between 0 and 60 days after billing).The historical records show that over the past 8 years,70 percent of the accounts have been current.The sample size needed in order to be 99% confident that the sample proportion of the current customer accounts is within .03 of the true proportion of all current accounts for this company would be _____.

A)1842
B)1549
C)897
D)632
E)1267

Question 65

The Ministry of Agriculture tested 105 fuel samples for accuracy of the reported octane level.For premium grade,14 out of 105 samples failed (they didn't meet specifications).The 99% confidence interval for the true population proportion of premium grade fuel-quality failures would be _____.

A)[.045,.221]
B)[.068,.198]
C)[.023,.115]
D)[.048,.219]
E)[.100,.276]

Question 66

A botanist measures the heights of 16 seedlings and obtains a mean and standard deviation of 72.5 cm and 4.5 cm,respectively.If seedling height is normally distributed,the 95% confidence interval for the mean height of seedlings in the population form which the sample was selected would be _____.

A)[62.91,82.09]
B)[70.30,74.70]
C)[70.10,74.90]
D)[70.54,74.46]
E)[71.90,73.10]

Question 67

In 2007,13,000 internet users were surveyed and asked about their willingness to pay fees for access to websites.Of these,2,938 were definitely not willing to pay such fees.The 95% confidence interval for the proportion definitely unwilling to pay fees would be _____.

A)[0.286,0.302]
B)[0.219,0.233]
C)[0.220,0.232]
D)[0.212,0.241]
E)[0.214,0.245]

Question 68

Recently,a case of food poisoning was traced to a particular restaurant chain.The source was identified and corrective actions were taken to make sure that the food poisoning would not reoccur.Despite the response from the restaurant chain,many consumers refused to visit the restaurant for some time after the event.A survey was conducted three months after the food poisoning occurred with a sample of 319 patrons contacted.Of the 319 contacted,29 indicated that they would not go back to the restaurant because of the potential for food poisoning.The 95% confidence interval for the true proportion of the market who still refuse to visit any of the restaurants in the chain three months after the event would be _____.

A)[.059,.122]
B)[.090,.091]
C)[.000,.196]
D)[.240,.339]
E)[.118,.244]

Question 69

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% and a standard deviation of 1.5%.If the percentage of contamination is normally distributed,the mean percentage of contamination removed at a 98% confidence level would be _____.

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 70

Scores on a standard IQ test are normally distributed with population standard deviation 15.How many random IQ scores must be obtained if we want to find the true population mean (with an allowable error of 0.5)and we want 97% confidence in the results?

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

Question 71

In a survey of 308 adults,17 listed jewellery among the romantic gifts men want to receive.The 98% confidence interval for the proportion of all adults who include jewellery among their responses would be _____.

A)[.025,.085]
B)[.169,.171]
C)[.120,.220]
D)[.140,.200]
E)[.050,.170]

Question 72

A 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.If the outstanding balance is normally distributed,the 90% confidence interval for the mean balance of defaulted loans over the past three years would be _____.

A)[66,487 69,349]
B)[39,299 96,537]
C)[57,329 78,507]
D)[61,829 74,007]
E)[61,519 74,317]

Question 73

In 2007,13,000 internet users were surveyed and asked about their willingness to pay fees for access to websites.Of these,2,938 were definitely not willing to pay such fees.How large a sample is necessary to estimate the proportion of interest to within 2% in a 95% confidence interval?

A)18
B)307
C)1680
D)2000
E)2965

Question 74

Recently,a case of food poisoning was traced to a particular restaurant chain.The source was identified and corrective actions were taken to make sure that the food poisoning would not reoccur.Despite the response from the restaurant chain,many consumers refused to visit the restaurant for some time after the event.What sample size would be needed in order to be 95% confident that the sample proportion is within 0.02 of p,the true proportion of customers who refuse to go back to the restaurant?

A)14
B)38
C)129
D)2401
E)1,777

Question 75

At a sobriety checkpoint,the police screened 676 drivers and 6 were arrested for impaired driving.The 92% confidence interval for the true proportion of drivers who were impaired at that time would be _____.

A)[0.000,0.027]
B)[0.003,0.015]
C)[0.902,0.938]
D)[0.000,0.076]
E)[0.006,0.030]

Question 76

In a manufacturing process,we are interested in measuring the average length of a certain type of bolt.Based on a preliminary sample of 9 bolts,the sample standard deviation is 0.3cm.If the lengths are normally distributed,how many bolts should be sampled in order to make us 95% confident that the sample mean bolt length is within 0.02cm of the true mean bolt length?

A)864.36
B)80
C)1470
D)3989
E)1197

Question 77

In a manufacturing process,we are interested in measuring the average length of a certain type of bolt.Past data indicates that the lengths are normally distributed with standard deviation 0.25cm.How many bolts should be sampled in order to make us 95% confident that the sample mean bolt length is within 0.02cm of the true mean bolt length?

A)25
B)49
C)423
D)601
E)1225

Question 78

To investigate the satisfaction level with garbage removal in an urban area,a telephone survey was taken of 100 residents.Seven residents reported being satisfied with their garbage removal.A 90% confidence interval for the true percentage of all satisfied residents would be _____.

A)[0.0000,0.2034]
B)[0.0371,0.1029]
C)[0.0039,0.1361]
D)[0.0280,0.1120]
E)[0.0078,0.1400]

Question 79

There are an average of 22.455 employees at 22 office furniture dealers in a province with a standard deviation of 18.52.If the number of employees can be approximated by a normal distribution,the 99% confidence interval for the true mean number of full-time employees at office furniture dealers would be _____.

A)[11.014,33.896]
B)[11.277,33.633]
C)[12.284,32.626]
D)[12.513,32.397]
E)[20.072,24.838]

Question 80

A manufacturer of soft dog treats establishes that,on average,13.5% of each treat contains "crude protein",with a standard deviation of $\sigma$
= 0)1%.When the process machine is properly calibrated,then this value is maintained,but uncontrollable factors such as moisture levels can alter the crude protein percentage.For quality control purposes,the manufacturer wishes to estimate the mean crude protein percentage to within 0.025% of its true value with a 99% confidence.If the percentage of "crude protein" is normally distributed,what sample size should be used?

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