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BUS/ST 350
PRACTICE PROBLEMS EXAM 3
Reiland
Exam date: Fri. 4/11
MATERIAL COVERED
:
topics
:
§4.2 p. 1820 Geometric Random Variables; §4.3 Normal Random Variables and their
Probability Distributions; §4.4 Sampling Distribution Models. §5.1 Point and Interval
Estimators: §5.2 Confidence Intervals for p; §5.3 Sample Size Required to Estimate p; §5.4
confidence Intervals for
.
::
"#
webassign homework
:
7, 8, 9, 10.
lecture worksheets
: 15  22.
a table of the normal distributions will be supplied with the test.
NOTE
:
these sample problems may not cover all topics for which you are responsible on exam 3.
WARNING!
1.
The owner of a small convenience store notices that only 5% of customers buy magazines.
a. What is the probability that the first customer to buy a magazine is the 4 customer?
>2
b. What is the probability that the first customer to buy a magazine is the 8 customer?
>2
c. How many customers should the owner expect until a customer buys a magazine?
2.
A random variable is normally distributed with
=100 and
=20. The median value is
.5
a) 100
b) 80
c) 120
d) cannot be determined
3.
Give the proportion of the area under the normal curve that lies within one standard deviation of the
mean.
a) 0.5000
b) 0.8413
c) 0.6826
d) cannot answer without knowing the value of the mean and the standard deviation.
4.
The mean SAT verbal score of next year's freshmen entering the local university is 600.
It is also known
that 69.5% of these freshmen have scores that are less than 625.
If the distribution of scores can be
modeled by a normal distribution, which of the following equations, when solved, will give the standard
deviation of the scores?
a)
(0.695)(0.305)(625)
È
b) 0.695 = (625600)/
5
c) 0.51 = (625600)/
5
d) 0.2549 = (625600)/
5
e) 1.25 = (625600)/
5
5.
The distribution of scores on a test can be modeled by a normal distribution with a standard deviation of
6.
Given that 93.32% of the students who took the test scored 90 or below, find the mean test score.
a) 90 + (0.9332)(6)
b) 90  (0.9332)(6)
c) 90 + (1.5)(6)
d) 90  (1.5)(6)
e) 90  (2)(6)
6.
The distribution of the times it takes a man to get to work is normal with a mean of 15 minutes and a
variance
of 4. The man is supposed to start work at 8:00 a.m.
At what time should he leave his house so
that he will be late only 4% of the time?
a) 8:00
b) 11.5 minutes before 8:00
c) 22 minutes before 8:00
d) 18.5 minutes before 8:00
e) 8 minutes before 8:00
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page 2
Practice Problems Exam 3
7.
The distribution of the times it takes a man to get to work is normal with a mean of 15 minutes and a
variance
of 4.
Suppose you observed the man one day and found that it took him 23 minutes to get to
work.
What could you infer or conclude?
a) The information given is correct because 23 would not be unusual.
b) There is not enough information given to make any conclusion.
c) That you have witnessed a rare event.
d) That the information about the distribution of the times it takes the man to get to work is
incorrect.
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 Spring '08
 reiland
 Business

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