c.
8/12
9. A very short quiz has one multiple-choice question with five possible choices (a, b, c, d, e) and one
true or false question. Assume you are taking the quiz but do not have any idea what the correct
answer is to either question, but you mark an answer anyway.
a.
What is the probability that you have given the correct answer to both questions?
b.
What is the probability that only one of the two answers is correct?
c.
What is the probability that neither answer is correct?
d.
What is the probability that only your answer to the multiple-choice question is correct?
e.
What is the probability that you have only answered the true or false question correctly?
a.
1/10
b.
5/10
c.
4/10
d.
1/10
4/10
10. Two of the cylinders in an eight-cylinder car are defective and need to be replaced. If two cylinders are
selected at random, what is the probability that
a.
both defective cylinders are selected?
b.
no defective cylinder is selected?
c.
at least one defective cylinder is selected?
a.
2/56
b.
30/56
c.
26/56
11. Assume two events A and B are mutually exclusive and, furthermore, P(A) = 0.2 and P(B) = 0.4.
a.
Find P(A B).
b.
Find P(A B).
c.
Find P(AB).
0.0
b.
0.6
0.0
12. You are given the following information on Events A, B, C, and D.
P(A) = .4
P(A D) = .6
P(A C) = .04
P(B) = .2
P(AB) = .3
P(A D) = .03
P(C) = .1
a.
Compute P(D).
b.
Compute P(A B).
c.
Compute P(AC).
d.
Compute the probability of the complement of C.
e.
Are A and B mutually exclusive? Explain your answer.
f.
Are A and B independent? Explain your answer.
g.
Are A and C mutually exclusive? Explain your answer.
h.
Are A and C independent? Explain your answer.
a.
0.23
b.
0.06
c.
0.4
d.
0.9
e.
No, P(AB) 0
No, P(AB) P(A)
g.
No, P(A C) 0
h.
Yes, P(A*C) = P(A)
13. A government agency has 6,000 employees. The employees were asked whether they preferred a four-
day work week (10 hours per day), a five-day work week (8 hours per day), or flexible hours. You are
given information on the employees’ responses broken down by gender.
Male
Female
Total
300
600
900
1,200
1,500
2,700
300
2,100
2,400
1,800
4,200
6,000
a.
What is the probability that a randomly selected employee is a man and is in favor of a four–
day work week?
b.
What is the probability that a randomly selected employee is female?
c.
A randomly selected employee turns out to be female. Compute the probability that she is in
favor of flexible hours.
d.
What percentage of employees is in favor of a five-day work week?
e.
Given that a person is in favor of flexible time, what is the probability that the person is
female?
f.
What percentage of employees is male and in favor of a five-day work week?
a.
0.05
b.
0.7
c.
0.5
d.
45%
e.
0.875
14. A bank has the following data on the gender and marital status of 200 customers.
Male
Female
Single
20
30
Married
100
50
a.
What is the probability of finding a single female customer?
b.
What is the probability of finding a married male customer?
c.
If a customer is female, what is the probability that she is single?
d.
What percentage of customers is male?
e.
If a customer is male, what is the probability that he is married?
f.
Are gender and marital status mutually exclusive?
g.
Is marital status independent of gender? Explain using probabilities.
a.
0.15
b.
0.5
c.
0.375
d.
60%
e.
0.833
No, the probability of intersection is not zero.
15. A survey of a sample of business students resulted in the following information regarding the genders
of the individuals and their major.
Major
Gender
Management
Marketing
Others
Total
Male
40
10
30
80
Female
30
20
70
120
Total
70
30
100
200
a.
What is the probability of selecting an individual who is majoring in Marketing?
b.
What is the probability of selecting an individual who is majoring in Management, given that
the person is female?
c.
Given that a person is male, what is the probability that he is majoring in Management?
d.
What is the probability of selecting a male individual?
a.
0.15
b.
0.25
c.
0.50
d.
0.40
16. The following table shows the number of students in three different degree programs and whether they
are graduate or undergraduate students:
Degree Program
Undergraduate
Graduate
Total
Business
150
50
200
Engineering
150
25
175
Arts & Sciences
100
25
125
Total
400
100
500
a.
What is the probability that a randomly selected student is an undergraduate?
b.
What percentage of students is engineering majors?
c.
If we know that a selected student is an undergraduate, what is the probability that he or she
is a business major?
d.
A student is enrolled in the Arts and Sciences school. What is the probability that the student
is an undergraduate student?
e.
What is the probability that a randomly selected student is a graduate Business major?
a.
0.8
b.
35%
c.
0.375
d.
0.8
e.
0.1
17. A small town has 5,600 residents. The residents in the town were asked whether or not they favored
building a new bridge across the river. You are given the following information on the residents’
responses, broken down by gender.
Men
Women
Total
In Favor
1,400
280
1,680
Opposed
840
3,080
3,920
Total
2,240
3,360
5,600
Let:
M be the event a resident is a man
W be the event a resident is a woman
F be the event a resident is in favor
P be the event a resident is opposed
a.
Find the joint probability table.
b.
Find the marginal probabilities.
c.
What is the probability that a randomly selected resident is a man and is in favor of building
the bridge?
d.
What is the probability that a randomly selected resident is a man?
e.
What is the probability that a randomly selected resident is in favor of building the bridge?
f.
What is the probability that a randomly selected resident is a man or in favor of building the
bridge or both?
g.
A randomly selected resident turns out to be male. Compute the probability that he is in
favor of building the bridge.
a. and b.
In Favor
Opposed
Total
c.
0.25
d.
0.4
0.3
0.45
g.
0.625
18. On a recent holiday evening, a sample of 500 drivers was stopped by the police. Three hundred were
under 30 years of age. A total of 250 were under the influence of alcohol. Of the drivers under 30
years of age, 200 were under the influence of alcohol.
Let A be the event that a driver is under the influence of alcohol.
Let Y be the event that a driver is less than 30 years old.
a.
Determine P(A) and P(Y).
b.
What is the probability that a driver is under 30 and not under the influence of alcohol?
c.
Given that a driver is not under 30, what is the probability that he/she is under the influence
of alcohol?
d.
What is the probability that a driver is under the influence of alcohol if we know the driver is
under 30?
e.
Show the joint probability table.
f.
Are A and Y mutually exclusive events? Explain.
g.
Are A and Y independent events? Explain.
b.
0.2
c.
0.25
d.
0.667
e.
19. Six vitamin and three sugar tablets identical in appearance are in a box. One tablet is taken at random
and given to Person A. A tablet is then selected and given to Person B.
What is the probability that
a.
Person A was given a vitamin tablet?
b.
Person B was given a sugar tablet given that Person A was given a vitamin tablet?
c.
neither was given vitamin tablets?
d.
both were given vitamin tablets?
e.
exactly one person was given a vitamin tablet?
f.
Person A was given a sugar tablet and Person B was given a vitamin tablet?
g.
Person A was given a vitamin tablet and Person B was given a sugar tablet?
a.
6/9
b.
3/8
c.
1/12
d.
5/12
e.
1/2
g.
1/4
20. In a random sample of UTC students 50% indicated they are business majors, 40% engineering
majors, and 10% other majors. Of the business majors, 60% were females; whereas, 30% of
engineering majors were females. Finally, 20% of the other majors were female.
a.
What percentage of students in this sample was female?
b.
Given that a person is female, what is the probability that she is an engineering major?
a.
44%
21. Sixty percent of the student body at UTC is from the state of Tennessee (T), 30% percent are from
other states (O), and the remainder is international students (I). Twenty percent of students from
Tennessee live in the dormitories, whereas 50% of students from other states live in the dormitories.
Finally, 80% of the international students live in the dormitories.
a.
What percentage of UTC students lives in the dormitories?
b.
Given that a student lives in the dormitory, what is the probability that she/he is an
international student?
c.
Given that a student does not live in the dormitory, what is the probability that she/he is an
international student?
a.
35%
b.
0.2286 (rounded)
c.
0.0308 (rounded)
22. Tammy is a general contractor and has submitted two bids for two projects (A and B). The probability
of getting project A is 0.65. The probability of getting project B is 0.77. The probability of getting at
least one of the projects is 0.90.
a.
What is the probability that she will get both projects?
b.
Are the events of getting the two projects mutually exclusive? Explain, using probabilities.
c.
Are the two events independent? Explain, using probabilities.
a.
0.52
b.
No, the probability of their intersection is not zero.
23. Assume you are taking two courses this semester (A and B). Based on your opinion, you believe the
probability that you will pass course A is 0.835; the probability that you will pass both courses is
0.276. You further believe the probability that you will pass at least one of the courses is 0.981.
a.
What is the probability that you will pass course B?
b.
Is the passing of the two courses independent events? Use probability information to justify
your answer.
c.
Are the events of passing the courses mutually exclusive? Explain.
d.
What method of assigning probabilities did you use?
a.
0.422
c.
No, the probability of their intersection is not zero.
d.
the subjective method
24. Assume you have applied to two different universities (let’s refer to them as Universities A and B) for
your graduate work. In the past, 25% of students (with similar credentials as yours) who applied to
University A were accepted, while University B accepted 35% of the applicants. Assume events are
independent of each other.
a.
What is the probability that you will be accepted in both universities?
b.
What is the probability that you will be accepted to at least one graduate program?
c.
What is the probability that one and only one of the universities will accept you?
d.
What is the probability that neither university will accept you?
a.
0.0875
b.
0.5125
d.
0.4875
25. Assume you have applied for two scholarships, a Merit scholarship (M) and an Athletic scholarship
(A). The probability that you receive an Athletic scholarship is 0.18. The probability of receiving both
scholarships is 0.11. The probability of getting at least one of the scholarships is 0.3.
a.
What is the probability that you will receive a Merit scholarship?
b.
Are events A and M mutually exclusive? Why or why not? Explain.
c.
Are the two events, A and M, independent? Explain, using probabilities.
d.
What is the probability of receiving the Athletic scholarship given that you have been awarded
the Merit scholarship?
e.
What is the probability of receiving the Merit scholarship given that you have been awarded
the Athletic scholarship?
0.23
d.
0.4783
e.
0.6111
26. In the two upcoming basketball games, the probability that UTC will defeat Marshall is 0.63, and the
probability that UTC will defeat Furman is 0.55. The probability that UTC will defeat both opponents
is 0.3465.
a.
What is the probability that UTC will defeat Furman given that they defeat Marshall?
b.
What is the probability that UTC will win at least one of the games?
c.
What is the probability of UTC winning both games?
d.
Are the outcomes of the games independent? Explain and substantiate your answer.
0.55
b.
0.8335
c.
0.3465
d.
Yes, the probability of defeating Furman (0.55) is equal to the probability of defeating Furman
27. The probability of an economic decline in the year 2013 is 0.23. There is a probability of 0.64 that we
will elect a republican president in the year 2012. If we elect a republican president, there is a 0.35
probability of an economic decline. Let “D” represent the event of an economic decline, and “R”
represent the event of election of a Republican president.
a.
Are “R” and “D” independent events?
b.
What is the probability of electing a Republican president in 2012 and an economic decline in
the year 2013?
c.
If we experience an economic decline in the year 2013, what is the probability that a
Republican president will have been elected in the year 2012?
d.
What is the probability of economic decline in 2013 or a Republican president elected in the
year 2012 or both?
b.
0.224
0.9739
d.
0.646
28. As a company manager for Claimstat Corporation there is a 0.40 probability that you will be promoted
this year. There is a 0.72 probability that you will get a promotion or a raise. The probability of getting
a promotion and a raise is 0.25.
a.
If you get a promotion, what is the probability that you will also get a raise?
b.
What is the probability of getting a raise?
c.
Are getting a raise and being promoted independent events? Explain using probabilities.
d.
Are these two events mutually exclusive? Explain using probabilities.
a.
0.625
b.
0.57
29. An applicant has applied for positions at Company A and Company B. The probability of getting an
offer from Company A is 0.4, and the probability of getting an offer from Company B is 0.3.
Assuming that the two job offers are independent of each other, what is the probability that
a.
the applicant gets an offer from both companies?
b.
the applicant will get at least one offer?
c.
the applicant will not be given an offer from either company?
d.
Company A does not offer the applicant a job, but Company B does?
a.
0.12
b.
0.58
c.
0.42
d.
0.18
30. A corporation has 15,000 employees. Sixty-two percent of the employees are male. Twenty-three
percent of the employees earn more than $30,000 a year. Eighteen percent of the employees are male
and earn more than $30,000 a year.
a.
If an employee is taken at random, what is the probability that the employee is male?
b.
If an employee is taken at random, what is the probability that the employee earns more than
$30,000 a year?
c.
If an employee is taken at random, what is the probability that the employee is male and earns
more than $30,000 a year?
d.
If an employee is taken at random, what is the probability that the employee is male or earns
more than $30,000 a year or both?
e.
The employee taken at random turns out to be male. Compute the probability that he earns
more than $30,000 a year.
f.
Are being male and earning more than $30,000 a year independent?
a.
0.62
b.
0.23
c.
0.18
e.
0.2903
31. A statistics professor has noted from past experience that a student who follows a program of studying
two hours for each hour in class has a probability of 0.9 of getting a grade of C or better, while a
student who does not follow a regular study program has a probability of 0.2 of getting a C or better. It
is known that 70% of the students follow the study program. Find the probability that if a student who
has earned a C or better grade, he/she followed the program.
32. A survey of business students who had taken the Graduate Management Admission Test (GMAT)
indicated that students who have spent at least five hours studying GMAT review guides have a
probability of 0.85 of scoring above 400. Students who do not spend at least five hours reviewing have
a probability of 0.65 of scoring above 400. It has been determined that 70% of the business students
spent at least five hours reviewing for the test.
a.
Find the probability of scoring above 400.
b.
Find the probability that given a student scored above 400, he/she spent at least five hours
reviewing for the test.
a.
0.79
b.
0.7532
33. A machine is used in a production process. From past data, it is known that 97% of the time the
machine is set up correctly. Furthermore, it is known that if the machine is set up correctly, it produces
95% acceptable (non-defective) items. However, when it is set up incorrectly, it produces only 40%
acceptable items.
a.
An item from the production line is selected. What is the probability that the selected item is
non-defective?
b.
Given that the selected item is non-defective, what is the probability that the machine is set up
correctly?
c.
What method of assigning probabilities was used here?
a.
0.9335
b.
0.9871
c.
the relative frequency method
34. In a recent survey in a Statistics class, it was determined that only 60% of the students attend class on
Fridays. From past data it was noted that 98% of those who went to class on Fridays pass the course,
while only 20% of those who did not go to class on Fridays passed the course.
a.
What percentage of students is expected to pass the course?
b.
Given that a person passes the course, what is the probability that he/she attended classes on
Fridays?
a.
66.8%
35. Thirty-five percent of the students who enroll in a statistics course go to the statistics laboratory on a
regular basis. Past data indicates that 40% of those students who use the lab on a regular basis make a
grade of B or better. On the other hand, 10% of students who do not go to the lab on a regular basis
make a grade of B or better. If a particular student made an A, determine the probability that she or he
used the lab on a regular basis.
36. In a city, 60% of the residents live in houses and 40% of the residents live in apartments. Of the people
who live in houses, 20% own their own business. Of the people who live in apartments, 10% own their
own business. If a person owns his or her own business, find the probability that he or she lives in a
house.
37. A market study taken at a local sporting goods store showed that of 20 people questioned, 6 owned
tents, 10 owned sleeping bags, 8 owned camping stoves, 4 owned both tents and camping stoves, and 4
owned both sleeping bags and camping stoves. Let Event A = owns a tent, Event B = owns a sleeping
bag, Event C = owns a camping stove, and Sample Space = 20 people questioned.
a. Find P(A), P(B), P(C), P(AÇC), P(BÇC).
b. Are the events A and C mutually exclusive? Explain briefly.
c. Are the events B and C independent events? Explain briefly.
d. If a person questioned owns a tent, what is the probability he also owns a camping stove?
e. If two people questioned own a tent, a sleeping bag, and a camping stove, how many own only a
camping stove?
f. Is it possible for 3 people to own both a tent and a sleeping bag, but not a camping stove?
38. The Board of Directors of Bidwell Valve Company has made the following estimates for the upcoming
year’s annual earnings:
P(earnings lower than this year) = .30
P(earnings about the same as this year) = .50
P(earnings higher than this year) = .20
After talking with union leaders, the human resource department has drawn the following conclusions:
P(Union will request wage increase | lower earnings next year) = .25
P(Union will request wage increase | same earnings next year) = .40
P(Union will request wage increase | higher earnings next year) = .90
a. Calculate the probability that the company earns the same as this year and the union requests a wage
increase.
b. Calculate the probability that the company has higher earnings next year and the union does not
request a wage increase.
c. Calculate the probability that the union requests a wage increase.
39. An accounting firm has noticed that of the companies it audits, 85% show no inventory shortages, 10%
show small inventory shortages and 5% show large inventory shortages. The firm has devised a new
accounting test for which it believes the following probabilities hold:
P(company will pass test | no shortage) = .90
P(company will pass test | small shortage) = .50
P(company will pass test | large shortage) = .20
a. If a company being audited fails this test, what is the probability of a large or small inventory
shortage?
b. If a company being audited passes this test, what is the probability of no inventory shortage?
40. Global Airlines operates two types of jet planes: jumbo and ordinary. On jumbo jets, 25% of the
passengers are on business while on ordinary jets 30% of the passengers are on business. Of Global’s
air fleet, 40% of its capacity is provided on jumbo jets. (Hint: you have been given two conditional
probabilities.)
a. What is the probability a randomly chosen business customer flying with Global is on a jumbo jet?
b. What is the probability a randomly chosen non-business customer flying with Global is on an
ordinary jet?
41. Safety Insurance Company has compiled the following statistics. For any one-year period:
P(accident | male driver under 25) = .22
P(accident | male driver over 25) = .15
P(accident | female driver under 25) = .16
P(accident | female driver over 25) = .14
The percentage of Safety’s policyholders in each category is:
Male Under 25 20%
Male Over 25 40%
Female Under 25 10%
Female Over 25 30%
a. What is the probability that a randomly selected policyholder will have an accident within the next
year?
b. Given that a driver has an accident, what is the probability the driver is a male over 25?
c. Given that a driver has no accident, what is the probability the driver is a female?
42. Super Cola sales breakdown as 80% regular soda and 20% diet soda. Men purchase 60% of the
regular soda, but only 30% of the diet soda. If a woman purchases Super Cola, what is the probability
that it is a diet soda?
43. An investment advisor recommends the purchase of shares in Infogenics, Inc. He has made the
following predictions:
P(Stock goes up 20% | Rise in GDP) = .6
P(Stock goes up 20% | Level GDP) = .5
P(Stock goes up 20% | Fall in GDP) = .4
An economist has predicted that the probability of a rise in the GDP is 30%, whereas the probability of
a fall in the GDP is 40%.
a. Draw a tree diagram to represent this multiple-step experiment.
b. What is the probability that the stock will go up 20%?
c. We have been informed that the stock has gone up 20%. What is the probability of a rise or fall in
the GDP?
44. The following probability model describes the number of snowstorms for Washington, D.C. for a
given year:
Number of
Snowstorms
0
1
2
3
4
5
6
Probability
.25
.33
.24
.11
.04
.02
.01
The probability of 7 or more snowstorms in a year is 0.
a. What is the probability of more than 2 but less than 5 snowstorms?
b. Given this a particularly cold year (in which 2 snowstorms have already been observed), what is the
conditional probability that 4 or more snowstorms will be observed?
c. If at the beginning of winter there is a snowfall, what is the probability of at least one more
snowstorm before winter is over?
45. The Ambell Company uses batteries from two different manufacturers. Historically, 60% of the
batteries are from manufacturer 1, and 90% of these batteries last for over 40 hours. Only 75% of the
batteries from manufacturer 2 last for over 40 hours. A battery in a critical tool fails at 32 hours.
What is the probability it was from manufacturer 2?
46. It is estimated that 3% of the athletes competing in a large tournament are users of an illegal drug to
enhance performance. The test for this drug is 90% accurate. What is the probability that an athlete
who tests positive is actually a user?
47. Through a telephone survey, a low-interest bank credit card is offered to 400 households. The
responses are as follows.
Income $50,000
Income >
$50,000
Accept offer
40
30
Reject offer
210
120
a. Develop a joint probability table and show the marginal probabilities..
b. What is the probability of a household whose income exceeds $50,000 and who rejects the offer?
c. If income is < $50,000, what is the probability the offer will be accepted?
d. If the offer is accepted, what is the probability that income exceeds $50,000?
Accept offer
Reject offer
48. There are two more assignments in a class before its end, and if you get an A on at least one of them,
you will get an A for the semester. Your subjective assessment of your performance is
Event
Probability
A on paper and A on exam
.25
A on paper only
.10
A on exam only
.30
A on neither
.35
a. What is the probability of getting an A on the paper?
b. What is the probability of getting an A on the exam?
c. What is the probability of getting an A in the course?
d. Are the grades on the assignments independent?
49. A marina has two party boats available for customers to rent. Historically, demand for party boats has
followed this distribution shown below. The revenue per rental is $400. If a customer wants a party
boat and none is available, the store gives a $150 coupon for jet ski rental.
Demand
Relative
Frequency
Revenue
Cost
0
.35
0
0
1
.30
400
0
2
.20
800
0
3
.10
800
150
4
.05
800
300
a. What is the expected demand?
b. What is the expected revenue?
c. What is the expected cost?
d. What is the expected profit?