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PAM 2100
Spring 2009
Problem Set #7
Answer Key
Total points: 10
#1) from the textbook:
7.38
Use df=1000.
Round your final answer to four decimal places.
(2 points)
(The actual degree of freedom of this problem is 14061=1405. But since we do not have
the tvalues for this df
in table D, we will use df=1000.)
The value of t , for df=1000 and
confidence level 99%, is 2.581.
So the confidence interval is
0675
.
9
.
3
1406
98
.
0
*
581
.
2
9
.
3
±
=
±
=
±
=
m
x
(
1 point for the correct value of t , 1 point for the correct margin of error)
(if someone uses n=1000 or 1001 by mistake, but the methods are otherwise correct, then
take only 1 point off)
#2) You will have complete sales information for last month in a week, but right now you
have data from a random sample of 31 stores.
The mean change in sales in the sample is
x
= 4.2 and the standard deviation of the changes in the
sample is
s
= 10.
Here are the
null and alternative hypotheses:
H
0
:
μ = 0
H
a
:
μ
≠
0
a) Find the tstatistic.
Round your answer to three decimal places, if necessary.
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 Spring '08
 ABDUS,S.

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