Statistics 2
1.
A 5 B 25 C 15 D 5
If one student is selected at random, what is the probability that
a. The student obtained a B ?
b. The student obtained either a A or a C ?
c. The student did not obtain a D ?
d. The student did not obtain either a B or a C ?
2. A realty company has 100 homes listed for sale. Some of these homes
have fireplaces, some have garages, and some have neither. A
breakdown is provided in the two way classification table below.
Fireplace No Fireplace
(F) (F)
____________________________________________________________________________
Garage (G) 50 30
No Garage (G) 10 10
a. If one of these 100 homes is selected at random,
i. What is the probability that the home selected does not have a
fireplace ?
ii. What is the probability that the home selected has a fireplace or
a garage ?
iii. What is the probability that the home selected has neither a
fireplace nor a garage ?
iv. What is the probability that the home selected has a garage but
not a fireplace ?
v. What is the probability that the home selected has a garage,
given that it has a fireplace?
b. Are the events F = Fireplace and G = Garage independent? Show
your proof.
C. Are the events F and G mutually exclusive? Why?
3. A person has applied for positions at company A, company B and
company C. The probability of obtaining an offer from company A is 0.4, from company B is 0.3 and from C is 0.6. Assume that the three job offers will be independent.
a. What is the probability that the person will receive job offers
from all three companies?
b. What is the probability that the person will receive a job offer
from company B only.
c. What is the probability that the person will receive a job offer
from at least one of the three companies?
d. What is the probability that the person will receive exactly one
job offer from the three companies?
HINT: Construct a tree diagram
4. A city council consists of 7 males and 4 females. Two councilors are
selected at random to represent the city at an Elton John concert.
What is the probability that
a. Both councilors are male?
b. One councilor is a male and one a female?
c. At least one councilor is a female?
NOTE: Express probabilities to 4 decimal places of accuracy.
HINT: Construct a tree diagram.
5. A machine used in a production process is set up correctly 97% of
the time. Given that the machine is set up correctly, only 5% of the
items it produces are defective, while 95% are not defective. On the
other hand, if the machine is set up incorrectly, 60% of the items it
produces are defective, while only 40% are not defective.
What is the probability that a randomly selected item from the
production process will not be defective?
NOTE: Express probabilities to 4 decimal places of accuracy.
HINT: Construct a tree diagram.
6. In a survey of 100 business executives, 60 percent were male and
40 percent were female. Seventy percent of the male executives used
a PDA (personal digital assistant). Overall, 60% of the executives
used a PDA. Construct a two-way classification table for the survey
results.
7. You are given the probabilities listed below.
P(A) = 0.25
P(B) = 0.30
P(C) = 0.55
P( A and C ) = 0.05
P( B and C ) = 0
P(B|A) = 0.48
a. Are A and B independent events? Why or why not?
b. Find P(A and B ).
c. Find P(A or B )
d. Find P(A|B).
e. Are B and C mutually exclusive events? Why or y not?
f. Are B and C independent events? Provide a mathematical proof.
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