Practice Questions 7
1.
You are interested in examining the salaries earned by graduate business school
students at the end of the first year after graduation.
In particular, you are interested in
seeing whether there is a difference between men and women graduates’ salaries.
From
a random sample of 55 women, you find the mean salary to be $47,520 with a standard
deviation of $5,633.
From a sample of 64 men, you find the mean salary to be $44,304
with a standard deviation of $4,793. What is the 95% confidence interval for the
difference between the population mean salary for men and women? Assume the
random sample observations are from normally distributed populations, and that the
population variances are assumed to be equal.
A)
$3,216 r
0.05
955
z
t
B)
$3,216 r
117,0.05
955
t
t
C)
$3,216 r
0.025
955
z
t
D)
$3,216 r
117,0.025
955
t
t
2.
In a recent survey of 240 teachers in Richmond, Virginia, 77.2% supported standardized
national testing of elementary students.
In a survey of 162 teachers in Raleigh, North
Carolina, 64.2% supported national testing.
Find a 99% confidence interval for the
difference between the two population proportions.
A)
0.13 r 0.119
B)
0.13 r 0.092
C)
0.13 r 0.135
D)
0.13 r 0.148
3.
You are interested in determining the average cost of a 3minute telephone call to
locations within the continental U.S. What sample size must you take to be 96% confident
that the results will be within $.75 of the true mean cost per call given that
7.71
σ
=
?
A)
185
B)
445
C)
406
D)
574
4.
Because of the popularity of movies as an entertainment medium for college students,
you plan to do a national study of the average cost of a movie ticket.
If you assume that
= $0.50, what sample size would you have to take to be 95% confident that your
estimate was within $0.25 of the true mean ticket prices?
A)
15
B)
7
C)
16
D)
8
5.
The Arkansas State Police wish to estimate the average mph being traveled on the
Interstate Highways, which cross the state.
If the estimate is to be within 8 mpg of the
true mean with 98% confidence and the population standard deviation is 22 mph, how
large a sample size must be taken?
A)
42
B)
15
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329
D)
14
6.
The pooled variance
2
p
s
is formed by combining information from two independent
samples.
If
2
1
s
=39,
2
2
s
= 25, and
1
2
,
n
n
=
then
2
p
s
is
A)
64
B)
8
C)
32
D)
14
7.
If we wish to construct a 95% confidence interval estimate for the difference between two
population proportions, then the confidence level would be
A)
1.96
B)
0.95
C)
0.475
D)
0.05
8.
In constructing 95% confidence interval estimate for the difference between the means of
two normally distributed populations, where the unknown population variances are
assumed not to be equal, summary statistics computed from two independent samples
are as follows:
50
1
=
n
,
175
1
=
x
,
5
.
18
1
=
s
,
42
2
=
n
,
158
2
=
x
, and
4
.
32
2
=
s
. The
upper confidence limit is:
A)
19.123
B)
28.212
C)
24.911
D)
5.788
9.
A researcher is interested in determining the proportion of college students who have
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 Spring '08
 YILMAZ
 Statistics, Normal Distribution, Standard Deviation, Statistical hypothesis testing

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