Witte & Witte, 9e
Chapter 8
Page 1 of 5 Pages
Chapter 8: Populations, Samples, and Probability
Exercise 1
For each of the following pairs, indicate with a Yes or No whether the relationship
between the first and second expressions could describe that between a sample and its
population, respectively.
a. Third graders in Minneapolis; third graders in Minnesota
b. Registered voters in Wisconsin; retirees residing in Wisconsin
c. Members of the University of Kentucky men’s basketball team; student athletes at
the University of Kentucky
d. History majors at Marquette University; history majors in the United States
e. Psychology majors in Connecticut; psychology majors at Yale University
f. Books written by Edgar Allan Poe; books written by American authors
g. Married women residing in Austin, Texas; married women residing in Texas.
h. Brad Pitt; Australian actors
Answers:
a. Yes
b. No
c. Yes
d. Yes
e. No
f. Yes
g. Yes
h. No
Exercise 2
Which of the following would be considered hypothetical populations?
a.
b.
c.
d.
e.
Persons who received a flu shot at a local hospital last October
Married couples who will still be married to each other in five years.
Persons who received a speeding ticket in Illinois last year
Freshmen students who will graduate from Ohio University within four years
Women who will suffer from severe depression sometime during their lives.
Answer:
b, d, and e are hypothetical populations
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Witte & Witte, 9e
Chapter 8
Page 2 of 5 Pages
Exercise 3
Dr. Sue Rogers needs four participants for a psychological experiment. She plans to
randomly select four persons from the group shown below. Indicate whether each of the
following statements is True or False.
Tom
George
Joe
Hank
Mary
Ellen
Jane
Sara
a. It is possible that the four persons in the sample would all be females.
b. It is possible that the sample would have two males and two females.
c. The random sample of four persons will accurately represent the important
features of the entire group.
d. Each person in the group has an equal chance of being selected.
Answers:
a. True
b. True
c. False
d. True
Exercise 4
The second and third lines from Table H Random Numbers are shown below. Use these
numbers to complete the random assignment of 18 subjects to three different
experimental treatment conditions: 1, 2, 3. Assign subjects in blocks of three so that
there will be equal numbers of subjects in each condition. Subject 1 is assigned to
condition 3, subject 2 is assigned to condition 2, and then subject 3 is assigned by default
to condition 1. Subject 4 is assigned to condition 2, subject 5 is assigned to condition 3,
and subject 6 is assigned by default to condition 1, and so on.
37542 04805 64864 74296 24805 24037 20636 10402 00822 91665
08422 68953 19645 09303 23209 02560 15953 34764 35080 33606
Subj.
No.
1
2
3
4
5
6
Subj.
Condition No.
3
7
2
8
1
9
2
10
3
11
1
12
Subj.
Condition No.
13
14
15
16
17
18
2
Condition
Witte & Witte, 9e
Chapter 8
Page 3 of 5 Pages
Answers:
Subj.
No.
1
2
3
4
5
6
Subj.
Condition No.
3
7
2
8
1
9
2
10
3
11
1
12
Subj.
Condition No.
2
13
3
14
1
15
1
16
2
17
3
18
Condition
2
1
3
2
3
1
Exercise 5
The weight distribution of the 80 Pittsburgh Steelers team members is shown below.
Source: http://www.steelers.com/team/player/
Lbs.
340-359
320-339
300-319
280-299
260-279
240-259
220-239
200-219
180-199
160-179
Frequency
2
6
8
8
4
9
13
14
15
1
a. If you randomly select one player, what is probability that the player weighs
between 300 lbs. and 319 lbs.?
b. If you randomly select one player, what is the probability that the player weighs
less than 200 lbs.?
c. If you randomly select one player, what is the probability that the player weighs
300 lbs. or more?
d. If you randomly select one player, what is the probability that the player weighs
more than 339 lbs. or less than 180 lbs.?
Answers:
a.
b.
c.
d.
8/80 = .1
16/80 = .2
16/80 = .2
2/80 + 1/80 = 3/80 = .0375
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Witte & Witte, 9e
Chapter 8
Page 4 of 5 Pages
Exercise 6
Tom has applied to the graduate programs of two universities: University A and
University B. Let’s say that probability that Tom will be accepted at University A is .60
and the probability that Tom will be accepted at University B is .35. Assume that the
acceptance decisions are independent of one another. What is the probability that
a. Tom will be accepted at both University A and University B?
b. Tom will be accepted at University A but not University B?
c. Tom will be accepted at University B but not University A?
Answers:
a. .60 × .35 = .21
b. .60 × .65 = .39
c. .35 × .40 = .14
Exercise 7
A small college reports that 55% of the student athletes on its campus are females. The
college also says that 32% of its athletes are on a basketball team and 23% of its athletes
are tennis players.
a. The conditional probability that an athlete is a tennis player, given that the athlete
is a female is 25%. If you randomly select one student athlete, what is the
probability that the athlete is a female tennis player?
b. The conditional probability that an athlete is a basketball player, given that the
athlete is a male is 30%. If you randomly select one student athlete, what is the
probability that the athlete is a male basketball player?
c. The conditional probability that the athlete is neither a tennis player nor a
basketball player, given that the athlete is a female is 42%. If you randomly
select one student athlete, what is the probability that the athlete is a female who
plays a sport other than tennis or basketball?
a. .55 × .25 = .14
b. .45 × .30 = .14
c. .55 × .42 = .23
Exercise 8
Referring to the standard normal table (Table A, Appendix C), find the probability that a
randomly selected z score will be
a. below -1.96
b. above 2.58
c. between -2.58 and 2.58
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Witte & Witte, 9e
Chapter 8
Page 5 of 5 Pages
Answers:
a. .025
b. .0049
c. .4951 × 2 = .9902
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