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 1 
BUAD 310 InClass Practice Solutions
9/8/10
1.
The Glitzwear catalog is mailed to thousands of people, and these people make (annually)
purchases from the catalog, which average $42 and have a standard deviation of $60.
a)
Assuming that the distribution is normal, find the probability that one person’s purchases will
exceed $40.
Soln:
40
42
P X
40
P Z
P Z
0.03
0.5
0.0120
0.5120
60
b)
Suppose that you would like to obtain a sample of 100 of these people for followup
interviews. For a sample of 100, what is the probability that the average annual purchases will
exceed $40?
Soln:
6293
.
0
1293
.
0
5
.
0
)
333
.
0
(
)
100
/
60
42
40
(
)
40
(
Z
P
Z
P
X
P
2.
A television cable company receives numerous phone calls throughout the day from customers
reporting service troubles and from wouldbe subscribers to the cable network. Most of these
callers are put "on hold" until a company operator is free to help them. The company has
determined that the length of time a caller is on hold is normally distributed with a mean of 3.1
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 Fall '07
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