PAM 210 Lecture 1
Problem Set #9
Posted: 14
th
April, 2008
Due date: 21
st
April, 2008
#1) 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.
Ans. The tstatistic is
338
.
2
31
/
10
0
2
.
4
≈

=
t
(10 points
. Full credit for the correct answer. 8 points if the final answer was wrong but
the formula was correct)
b) Is the result statistically significant at the 1% level?
Ans. The df =311=30. Since this is a twosided test, the critical value is
75
.
2
)
30
(
005
.
0
=
t
.
Since 2.338<2.75, the result is not significant
at the 1% level.
(10 points.
Full credit if the final answer is correct (significant/not significant). If the
final answer is wrong, then 5 points for correct df, and
3 more points for the correct
critical value)
#2) A bank wonders whether omitting the annual credit card fee for customers who
charge at least three thousand dollars in a year would increase the amount charged on its
credit card.
The bank makes this offer to an SRS of 1001 of its existing credit card
customers.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '08
 ABDUS,S.
 Statistics, 1%, $200, cocaine, $15, 6year

Click to edit the document details