This document contains several statistics exercises involving calculating point estimates, confidence intervals, and other inferential statistics concepts. The exercises provide sample data and ask the reader to calculate things like means, variances, standard errors, and confidence intervals. They cover topics like using sample data to estimate properties of populations, constructing confidence intervals for means and proportions, and applying these statistical techniques to real-world scenarios.

1. Exercise 7.2
Self­Check Exercises
SC 7-1 The Greensboro Coliseum is considering expanding its seating capacity and needs to know
both the average number of people who attend events there and the variability in this number.
The following are the attendances (in thousands) at nine randomly selected sporting events.
Find point estimates of the mean and the variance of the population from which the sample
was draw
8.8 14.0 21.3 7.9 12.5 20.6 16.3 14.1 13.0
SC 7-2 The Pizza Distribution Authority (PDA) has developed quite a business in Carrboro by
delivering pizza orders promptly. PDA guarantees that its pizzas will be delivered in 30
minutes or less from the time the order was placed, and if the delivery is late, the pizza is
free. The time that it takes to deliver each pizza order that is on time is recorded in the
Official Pizza Time Book (OPTB), and the delivery time for those pizzas that are delivered
late is recorded as
30 minutes in the OPTB. Twelve random entries from the OPTB are listed.
15.3 29.5 30.0 10.1 30.0 19.6
10.8 12.2 14.8 30.0 22.1 18.3
(a) Find the mean for the sample.
(b) From what population was this sample drawn?
(c) Can this sample be used to estimate the average time that it takes for PDA to deliver a
pizza? Explain.
Applications
7-7 Joe Jackson, a meteorologist for local television station WDUL, would like to report the
average rainfall for today on this evening’s newscast. The following are the rainfall
measurements (in inches) for today’s date for 16 randomly chosen past years. Determine the
sample mean rainfall.
0.47 0.27 0.13 0.54 0.00 0.08 0.75 0.06
0.00 1.05 0.34 0.26 0.17 0.42 0.50 0.86
7-8 The National Bank of Lincoln is trying to determine the number of tellers available during
the lunch rush on Fridays. The bank has collected data on the number of people who entered
the bank during the last 3 months on Friday from 11 A.M. to 1 P.M. Using the data below, find
point estimates of the mean and standard deviation of the population from which the sample
was drawn.
242 275 289 306 342 385 279 245 269 305 294 328
7-9 Electric Pizza was considering national distribution of its regionally successful product and
was compiling pro forma sales data. The average monthly sales figures (in thousands of
dollars) from its 30 current distributors are listed. Treating them as (a) a sample and (b) a
population, compute the standard deviation.
7.3 5.8 4.5 8.5 5.2 4.1
2.8 3.8 6.5 3.4 9.8 6.5
6.7 7.7 5.8 6.8 8.0 3.9
6.9 3.7 6.6 7.5 8.7 6.9
2.1 5.0 7.5 5.8 6.4 5.2

2. 7-10 In a sample of 400 textile workers, 184 expressed extreme dissatisfaction regarding a
prospective plan to modify working conditions. Because this dissatisfaction was strong
enough to allow management to interpret plan reaction as being highly negative, they were
curious about the proportion of total workers harboring this sentiment. Give a point estimate
of this proportion.
7-11 The Friends of the Psychics network charges $3 per minute to learn the secrets that can turn
your life around. The network charges for whole minutes only and rounds up to benefit the
company. Thus, a 2 minute 10 second call costs $9. Below is a list of 15 randomly selected
charges.
3 9 15 21 42 30 6 9 6 15 21 24 32 9 12
(a) Find the mean of the sample.
(b) Find a point estimate of the variance of the population.
(c) Can this sample be used to estimate the average length of a call? If so, what is your
estimate? If not, what can we estimate using this sample?
Exercise 7.3
elf­Check Exercises
SC 7-3 For a population with a known variance of 185, a sample of 64 individuals leads to 217 as an
estimate of the mean.
(a) Find the standard error of the mean.
(b) Establish an interval estimate that should include the population mean 68.3 percent of the
time.
SC 7-4 Eunice Gunterwal is a frugal undergraduate at State U. Who is interested in purchasing a used
car. She randomly selected 125 want ads and found that the average price of a car in this
sample was $3,250. Eunice knows that the standard deviation of used-car prices in this city is
$615.
(a) Establish an interval estimate for the average price of a car so that Eunice can be 68.3
percent certain that the population mean lies within this interval.
(b) Establish an interval estimate for the average price of a car so that Miss Gunterwal can be
95.5 percent certain that the population mean lies within this interval.
Basic Concepts
7-12 From a population known to have a standard deviation of 1.4, a sample of 60 individuals is
taken. The mean for this sample is found to be 6.2.
(a) Find the standard error of the mean.
(b) Establish an interval estimate around the sample mean, using one standard error of
the mean.
7-13 From a population with known standard deviation of 1.65, a sample of 32 items resulted in
34.8 as an estimate of the mean.
(a) Find the standard error of the mean.
(b) Compute an interval estimate that should include the population mean 99.7 percent of
the time.
Applications
7-14 The University of North Carolina is conducting a study on the average weight of the many
bricks that make up the University’s walkways. Workers are sent to dig up and weigh a
sample of 421 bricks and the average brick weight of this sample was 14.2 lb. It is a well-
known fact that the standard deviation of brick weight is 0.8 lb.

3. (a) Find the standard error of the mean.
(b) What is the interval around the sample mean that will include the population mean
95.5 percent of the time?
7-15 Because the owner of the Bard’s Nook, a recently opened restaurant, has had difficulty
estimating the quantity of food to be prepared each evening, he decided to determine the
mean number of customers served each night. He selected a sample of 30 nights, which
resulted in a mean of 71. The population standard deviation has been established as 3.76.
(a) Give an interval estimate that has a 68.3 percent probability of including the population
mean.
(b) Give an interval estimate that has a 99.7 percent chance of including the population
mean.
7-16 The manager of the Neuse River Bridge is concerned about the number of cars “running” the
toll gates and is considering altering the toll-collection procedure if such alteration would be
cost-effective. She randomly sampled 75 hours to determine the rate of violation. The
resulting average violations per hour was 7. If the population standard deviation is known to
be 0.9, estimate an interval that has a 95.5 percent chance of containing the true mean.
7-17 Gwen Taylor, apartment manager for WillowWood Apartments, wants to inform potential
renters about how much electricity they can expect to use during August. She randomly
selects 61 residents and discovers their average electricity usage in August to be 894 kilowatt
hours (kwh). Gwen believes the variance in usage is about 131 (kwh)2
.
(a) Establish an interval estimate for the average August electricity usage so Gwen can be
68.3 percent certain the true population mean lies within this interval.
(b) Repeat part (a) with a 99.7 percent certainty.
(c) If the price per kwh is $0.12, within what interval can Gwen be 68.3 percent certain that
the average August cost for electricity will lie?
7-18 The school board of Forsight County considers its most important task to be keeping the
average class size in Forsight County schools less than the average class size in neighboring
Hindsight County. Miss Dee Marks, the school superintendent for Forsight County, has just
received reliable information indicating that the average class size in Hindsight County this
year is 30.3 students. She does not yet have the figures for all 621 classes in her own school
system, so Dee is forced to rely upon the 76 classes that have reported class sizes, yielding an
average class size of 29.8 students. Dee knows that the class size of Forsight County classes
has a distribution with an unknown mean and standard deviation equal to 8.3 students.
Assuming that the sample of 76 that Miss Marks possesses is randomly chosen from the
population of all Forsight County class sizes:
(a) Find an interval that Dee can be 95.5 percent certain will contain the true mean.
(b) Do you think that Dee has met her goal?
Exercise 7.4
Self­Check Exercise
SC 7-5 Given the following confidence levels, express the lower and upper limits of the confidence
interval for these levels in terms of x and s x
.
(a) 54 percent.
(b) 75 percent.
(c) 94 percent.
(d) 98 percent.
Basic Concepts
7-19 Define the confidence level for an interval estimate.
7-20 Define the confidence interval.
7-21 Suppose you wish to use a confidence level of 80 percent. Give the upper limit of the
confidence interval in terms of the sample mean, x, and the standard error, s x
.
7-22 In what way may an estimate be less meaningful because of

4. (a) A high confidence level?
(b) A narrow confidence interval?
7-23 Suppose a sample of 50 is taken from a population with standard deviation 27 and that the
sample mean is 86.
(a) Establish an interval estimate for the population mean that is 95.5 percent certain to
include the true population mean.
(b) Suppose, instead, that the sample size was 5,000. Establish an interval for the population
mean that is 95.5 percent certain to include the true population mean.
(c) Why might estimate (a) be preferred to estimate (b)? Why might (b) be preferred to (a)?
7-24 Is the confidence level for an estimate based on the interval constructed from a single
sample?
7-25 Given the following confidence levels, express the lower and upper limits of the confidence
interval for these levels in terms of x and s x
.
(a) 60 percent.
(b) 70 percent.
(c) 92 percent.
(d) 96 percent.
Applications
7-26 Steve Klippers, owner of Steve’s Barbershop, has built quite a reputation among the residents of
Cullowhee. As each customer enters his barbershop, Steve yells out the number of minutes that
the customer can expect to wait before getting his haircut. The only statistician in town, after
being frustrated by Steve’s inaccurate point estimates, has determined that the actual waiting
time for any customer is normally distributed with mean equal to Steve’s estimate in minutes
and standard deviation equal to 5 minutes divided by the customer’s position in the waiting line.
Help Steve’s customers develop 95 percent probability intervals for the following situations·
(a) The customer is second in line and Steve’s estimate is 25 minutes.
(b) The customer is third in line and Steve’s estimate is 15 minutes.
(c) The customer is fifth in line and Steve’s estimate is 38 minutes.
(d) The customer is first in line and Steve’s estimate is 20 minutes.
(e) How are these intervals different from confidence intervals?
Exercise 7.5
Self­Check Exercises
SC 7-6 From a population of 540, a sample of 60 individuals is taken. From this sample, the mean is
found to be 6.2 and the standard deviation 1.368.
(a) Find the estimated standard error of the mean.
(b) Construct a 96 percent confidence interval for the mean.
SC 7-7 In an automotive safety test conducted by the North Carolina Highway Safety Research
Center, the average tire pressure in a sample of 62 tires was found to be 24 pounds per square
inch, and the standard deviation was 2.1 pounds per square inch.
(a) What is the estimated population standard deviation for this population? (There are about
a million cars registered in North Carolina.)
(b) Calculate the estimated standard error of the mean.
(c) Construct a 95 percent confidence interval for the population mean.
Basic Concepts
7-27 The manager of Cardinal Electric’s lightbulb division must estimate the average number of

5. hours that a lightbulb made by each lightbulb machine will last. A sample of 40 lightbulbs
was selected from machine A and the average burning time was 1,416 hours. The standard
deviation of burning time is known to be 30 hours.
(a) Compute the standard error of the mean.
(b) Construct a 90 percent confidence interval for the true population mean.
7-28 Upon collecting a sample of 250 from a population with known standard deviation of 13.7,
the mean is found to be 112.4.
(a) Find a 95 percent confidence interval for the mean.
(b) Find a 99 percent confidence interval for the mean.
Applications
7-29 The Westview High School nurse is interested in knowing the average height of seniors at
this school, but she does not have enough time to examine the records of all 430 seniors. She
randomly selects 48 students. She finds the sample mean to be 64.5 inches and the standard
deviation to be 2.3 inches.
(a) Find the estimated standard error of the mean.
(b) Construct a 90 percent confidence interval for the mean.
7-30 Jon Jackobsen, an overzealous graduate student, has just completed a first draft of his 700-
page dissertation. Jon has typed his paper himself and is interested in knowing the average
number of typographical errors per page, but does not want to read the whole paper. Knowing
a little bit about business statistics, Jon selected 40 pages at random to read and found that the
average number of typos per page was 4.3 and the sample standard deviation was 1.2 typos
per page.
(a) Calculate the estimated standard error of the mean.
(b) Construct for Jon a 90 percent confidence interval for the true average number of typos
per page in his paper.
7-31 The Nebraska Cable Television authority conducted a test to determine the amount of time
people spend watching television per week. The NCTA surveyed 84 subscribers and found
the average number of hours watched per week to be 11.6 hours and the standard deviation to
be 1.8 hours.
(a) What is the estimated population standard deviation for this population? (There are about
95,000 people with cable television in Nebraska.)
(b) Calculate the estimated standard error of the mean.
(c) Construct a 98 percent confidence interval for the population mean.
7-32 Joel Friedlander is a broker on the New York Stock Exchange who is curious about the
amount of time between the placement and execution of a market order. Joel sampled 45
orders and found that the mean time to execution was 24.3 minutes and the standard deviation
was 3.2 minutes. Help Joel by constructing a 95 percent confidence interval for the mean
time to execution.
7-33 Oscar T. Grady is the production manager for Citrus Groves Inc., located just north of Ocala,
Florida. Oscar is concerned that the last 3 years’ late freezes have damaged the 2,500 orange
trees that Citrus Groves owns. In order to determine the extent of damage to the trees, Oscar
has sampled the number of oranges produced per tree for 42 trees and found that the average
production was 525 oranges per tree and the standard deviation was 30 oranges per tree.
(a) Estimate the population standard deviation from the sample standard deviation.
(b) Estimate the standard error of the mean for this finite population.
(c) Construct a 98 percent confidence interval for the mean per-tree output of all 2,500 trees.
(d) If the mean orange output per tree was 600 oranges 5 years ago, what can Oscar say
about the possible existence of damage now?
7-34 Chief of Police Kathy Ackert has recently instituted a crackdown on drug dealers in her city.
Since the crackdown began, 750 of the 12,368 drug dealers in the city have been caught. The
mean dollar value of drugs found on these 750 dealers is $250,000. The standard deviation of
the dollar value of drugs for these 750 dealers is $41,000. Construct for Chief Ackert a 90
percent confidence interval for the mean dollar value of drugs possessed by the city’s drug
dealers.

6. Exercise 7.6
Self­Check Exercises
SC 7-8 When a sample of 70 retail executives was surveyed regarding the poor November
performance of the retail industry, 66 percent believed that decreased sales were due to
unseasonably warm temperatures, resulting in consumers’ delaying purchase of cold-weather
items.
(a) Estimate the standard error of the proportion of retail executives who blame warm
weather for low sales.
(b) Find the upper and lower confidence limits for this proportion, given a 95 percent
confidence level.
SC 7-9 Dr. Benjamin Shockley, a noted social psychologist, surveyed 150 top executives and found
that 42 percent of them were unable to add fractions correctly.
(a) Estimate the standard error of the proportion.
(b) Construct a 99 percent confidence interval for the true proportion of top executives who
cannot correctly add fractions.
Applications
7-35 Pascal, Inc., a computer store that buys wholesale, untested computer chips, is considering
switching to another supplier who would provide tested and guaranteed chips for a higher
price. In order to determine whether this is a cost-effective plan, Pascal must determine the
proportion of faulty chips that the current supplier provides. A sample of 200 chips was tested
and of these, 5 percent were found to be defective.
(a) Estimate the standard error of the proportion of defective chips.
(b) Construct a 98 percent confidence interval for the proportion of defective chips supplied.
7-36 General Cinema sampled 55 people who viewed GhostHunter 8 and asked them whether they
planned to see it again. Only 10 of them believed the film was worthy of a second look.
(a) Estimate the standard error of the proportion of moviegoers who will view the film a
second time.
(b) Construct a 90 percent confidence interval for this proportion.
7-37 The product manager for the new lemon-lime Clear ’n Light dessert topping was
worried about both the product’s poor performance and her future with Clear ’n Light.
Concerned that her marketing strategy had not properly identified the attributes of the
product, she sampled 1,500 consumers and learned that 956 thought that the product
was a floor wax.
(a) Estimate the standard error of the proportion of people holding this severe misconception
about the dessert topping.
(b) Construct a 96 percent confidence interval for the true population proportion.
7-38 Michael Gordon, a professional basketball player, shot 200 foul shots and made 174 of them.
(a) Estimate the standard error of the proportion of all foul shots Michael makes.
(b) Construct a 98 percent confidence interval for the proportion of all foul shots Michael
makes.
7-39 SnackMore recently surveyed 95 shoppers and found 80 percent of them purchase
SnackMore fat-free brownies monthly.
(a) Estimate the standard error of the proportion.
(b) Construct a 95 percent confidence interval for the true proportion of people who purchase
the brownies monthly.
7-40 The owner of the Home Loan Company randomly surveyed 150 of the company’s 3,000
accounts and determined that 60 percent were in excellent standing.
(a) Find a 95 percent confidence interval for the proportion in excellent standing.
(b) Based on part (a), what kind of interval estimate might you give for the absolute number
of accounts that meet the requirement of excellence, keeping the same 95 percent confidence
level?
7-41 For a year and a half, sales have been falling consistently in all 1,500 franchises of a fast-food
chain. A consulting firm has determined that 31 percent of a sample of 95 indicate clear signs
of mismanagement. Construct a 98 percent confidence interval for this proportion.

7. 7-42 Student government at the local university sampled 45 textbooks at the University
Student Store and determined that of these 45 textbooks, 60 percent had been marked up
in price more than 50 percent over wholesale cost. Give a 96 percent confidence interval
for the proportion of books marked up more than 50 percent by the University Student
Store.
7-43 Barry Turnbull, the noted Wall Street analyst, is interested in knowing the proportion of
individual stockholders who plan to sell at least one-quarter of all their stock in the next
month. Barry has conducted a random survey of 800 individuals who hold stock and has
learned that 25 percent of his sample plan to sell at least one-quarter of all their stock in
the next month. Barry is about to issue his much-anticipated monthly report, “The Wall
Street Pulse—the Tape’s Ticker,” and would like to be able to report a confidence
interval to his subscribers. He is more worried about being correct than he is about the
width of the interval. Construct a 90 percent confidence interval for the true proportion
of individual stockholders who plan to sell at least one-quarter of their stock during the
next month.
Exercise 7.7
Self­Check Exercises
SC 7-10 For the following sample sizes and confidence levels, find the appropriate t values for
constructing confidence intervals:
(a) n  28; 95 percent.
(b) n  8; 98 percent.
(c) n  13; 90 percent.
(d) n  10; 95 percent.
(e) n  25; 99 percent.
(f) n  10; 99 percent.
SC 7-11 Seven homemakers were randomly sampled, and it was determined that the distances they
walked in their housework had an average of 39.2 miles per week and a sample standard
deviation of 3.2 miles per week. Construct a 95 percent confidence interval for the population
mean.
Basic Concepts
7-44 For the following sample sizes and confidence levels, find the appropriate t values for
constructing confidence intervals:
(a) n  15; 90 percent.
(b) n  6; 95 percent.
(c) n  19; 99 percent.
(d) n  25; 98 percent.
(e) n  10; 99 percent.
(f) n  41; 90 percent.
7-45 Given the following sample sizes and t values used to construct confidence intervals, find the
corresponding confidence levels:
(a) n  27; t  ±2.056.
(b) n  5; t  ±2.132.
(c) n  18; t  ±2.898.
7-46 A sample of 12 had a mean of 62 and a standard deviation of 10. Construct a 95 percent
confidence interval for the population mean.
7-47 The following sample of eight observations is from an infinite population with a normal
distribution:
75.3 76.4 83.2 91.0 80.1 77.5 84.8 81.0
(a) Find the sample mean.

8. (b) Estimate the population standard deviation.
(c) Construct a 98 percent confidence interval for the population mean.
Applications
7-48 Northern Orange County has found, much to the dismay of the county commissioners, that
the population has a severe problem with dental plaque. Every year the local dental board
examines a sample of patients and rates each patient’s plaque buildup on a scale from 1 to
100, with 1 representing no plaque and 100 representing a great deal of plaque. This year, the
board examined 21 patients and found that they had an average Plaque Rating Score (PRS) of
72 and a standard deviation of 6.2. Construct for Orange County a 98 percent confidence
interval for the mean PRS for Northern Orange County.
7-49 Twelve bank tellers were randomly sampled and it was determined they made an average of
3.6 errors per day with a sample standard deviation of 0.42 error. Construct a 90 percent
confidence interval for the population mean of errors per day. What assumption is implied
about the number of errors bank tellers make?
7-50 State Senator Hanna Rowe has ordered an investigation of the large number of boating
accidents that have occurred in the state in recent summers. Acting on her instructions, her
aide, Geoff Spencer, has randomly selected 9 summer months within the last few years and
has compiled data on the number of boating accidents that occurred during each of these
months. The mean number of boating accidents to occur in these 9 months was 31, and the
standard deviation in this sample was 9 boating accidents per month. Geoff was told to
construct a 90 percent confidence interval for the true mean number of boating accidents per
month, but he was in such an accident himself recently, so you will have to do this for him.
Exercise 7.8
Self­Check Exercises
SC 7-12 For a test market, find the sample size needed to estimate the true proportion of consumers
satisfied with a certain new product within ±0.04 at the 90 percent confidence level. Assume
you have no strong feeling about what the proportion is.
SC 7-13 A speed-reading course guarantees a certain reading rate increase within 2 days. The teacher
knows a few people will not be able to achieve this increase, so before stating the guaranteed
percentage of people who achieve the reading rate increase, he wants to be 98 percent
confident that the percentage has been estimated to within ±5 percent of the true value. What
is the most conservative sample size needed for this problem?
Basic Concepts
7-51 If the population standard deviation is 78, find the sample size necessary to estimate the true
mean within 50 points for a confidence level of 95 percent.
7-52 We have strong indications that the proportion is around 0.7. Find the sample size needed to
estimate the proportion within ±0.02 with a confidence level of 90 percent.
7-53 Given a population with a standard deviation of 8.6, what size sample is needed to estimate
the mean of the population within ±0.5 with 99 percent confidence?
Applications
7-54 An important proposal must be voted on, and a politician wants to find the proportion of
people who are in favor of the proposal. Find the sample size needed to estimate the true
proportion to within ±.05 at the 95 percent confidence level. Assume you have no strong

9. feelings about what the proportion is. How would your sample size change if you believe
about 75 percent of the people favor the proposal? How would it change if only about 25
percent favor the proposal?
7-55 The management of Southern Textiles has recently come under fire regarding the supposedly
detrimental effects on health caused by its manufacturing process. A social scientist has
advanced a theory that the employees who die from natural causes exhibit remarkable
consistency in their life-span: The upper and lower limits of their life-spans differ by no more
than 550 weeks (about 10½ years). For a confidence level of 98 percent, how large a sample
should be examined to find the average life-span of these employees within ±30 weeks?
7-56 Food Tiger, a local grocery store, sells generic garbage bags and has received quite a few
complaints about the strength of these bags. It seems that the generic bags are weaker than the
name-brand competitor’s bags and, therefore, break more often. John C. Tiger, VP in charge
of purchasing, is interested in determining the average maximum weight that can be put into
one of the generic bags without its breaking. If the standard deviation of garbage breaking
weight is 1.2 lb, determine the number of bags that must be tested in order for Mr. Tiger to be
95 percent confident that the sample average breaking weight is within 0.5 lb of the true
average.
7-57 The university is considering raising tuition to improve school facilities, and they want to
determine what percentage of students favor the increase. The university needs to be 90
percent confident the percentage has been estimated to within 2 percent of the true value.
How large a sample is needed to guarantee this accuracy regardless of the true percentage?
7-58 A local store that specializes in candles and clocks, Wicks and Ticks, is interested in obtaining
an interval estimate for the mean number of customers that enter the store daily. The owners
are reasonably sure that the actual standard deviation of the daily number of customers is 15
customers. Help Wicks and Ticks out of a fix by determining the sample size it should use in
order to develop a 96 percent confidence interval for the true mean that will have a width of
only eight customers.
Chapter Concepts Test
Circle the correct answer or fill in the blank. Answers are in the back of the book.
T F 1. A statistic is said to be an efficient estimator of a population parameter if, with
increasing sample size, it becomes almost certain that the value of the statistic
comes very close to that of the population parameter.
T F 2. An interval estimate is a range of values used to estimate the shape of a population’s
distribution.
T F 3. If a statistic tends to assume values higher than the population parameter as
frequently as it tends to assume values that are lower, we say that the statistic is an
unbiased estimate of the parameter.
T F 4. The probability that a population parameter will lie within a given interval estimate
is known as the confidence level.
T F 5. With increasing sample size, the t distribution tends to become flatter in shape.
T F 6. We must always use the t distribution, rather than the normal, whenever the standard
deviation of the population is not known.
T F 7. We may obtain a crude estimate of the standard deviation of some population if we
have some information about its range.
T F 8. When using the t distribution in estimation, we must assume that the population is
approximately normal,

10. T F 9. Using high confidence levels is not always desirable because high confidence levels
produce large confidence intervals.
T F 10. There is a different t distribution for each possible sample size.
T F 11. A point estimate is often insufficient because it is either right or wrong.
T F 12. A sample mean is said to be an unbiased estimator of a population mean because no
other estimator could extract from the sample additional information about the
population mean.
T F 13. The most frequently used estimator of  is s.
T F 14. The standard error of the proportion is calculated as
T F 15. The degrees of freedom used in a t-distribution estimation are equal to the sample
size.
T F 16. The t distribution is less able to be approximated by a normal distribution as the
sample size increases.
T F 17. The t distribution need not be used in estimating if you know the standard deviation
of the population.
T F 18. The sample median is always the best estimator of the population median.
T F 19. As the width of a confidence interval increases, the confidence level associated with
the interval also increases.
T F 20. Estimating the standard error of the mean of a finite population using an estimate of
the population standard deviation requires the use of the t distribution for calculating
subsequent confidence intervals.
T F 21. The percentages in the t distribution table correspond to the chance that the true
population parameter will fall outside our confidence interval.
T F 22. In a normal distribution, 100 percent of the population lies within ±3 standard
deviations of the mean.
A B C D E 23.
When choosing an estimator of a population parameter, one should consider:
(a) Sufficiency.
(b) Clarity.
(c) Efficiency.
(d) All of these.
(e) (a) and (c) but not (b).
A B C D E 24.
Suppose that 200 members of a group were asked whether they like a particular
product. Fifty said yes; 150 said no. Assuming “yes” means a success, which of the
following is correct?
(a) = 0.33.
(b) = 0.25.
(c) p = 0.33.
(d) p = 0.25.
(e) (b) and (d) only.

11. A B C D 25. Assume that you take a sample and calculate as 100. You then calculate the upper
limit of a 90 percent confidence interval for ; its value is 112. What is the lower
limit of this confidence interval?
(a)
44. Theoretically, the _________________________ distribution is the correct distribution to use in
constructing confidence intervals to estimate a population proportion.
45. In the absence of additional information, a value of _________________________
should be used for p when determining a sample size for estimating a population
proportion.