Section 8.6
Exercise 8.39
.
1
2
is approximately
given by
(
x
1
x
2
)
±
1
:
96
s
s
2
1
n
1
+
s
2
2
n
2
.
(
a
) If
n
1
= 35,
n
2
= 49,
x
1
= 12
:
7,
x
2
= 7
:
4,
s
2
1
= 1
:
38,
s
2
2
= 4
:
14, then
(12
:
7
7
:
4)
±
1
:
96
s
1
:
38
35
+
4
:
14
49
= 5
:
3
±
0
:
690
or
4
:
61
1
2
<
5
:
99.
(
b
) Because the value
1
2
likely that
1
=
2
. We should conclude that there is a di±erence in the two
population means.
Exercise 8.41
.
1
2
is approximately
given by
(
x
1
x
2
)
±
1
:
96
s
s
2
1
n
1
+
s
2
2
n
2
.
(
a
) If
n
1
= 30,
n
2
= 30,
x
1
= 167
:
1,
x
2
= 140
:
9,
s
1
= 24
:
3,
s
2
= 17
:
6, then
(167
:
1
140
:
9)
±
1
:
96
s
(24
:
3)
2
30
+
(17
:
6)
2
30
= 26
:
2
±
2
:
316
or
15
:
463
1
2
<
36
:
937.
(
b
) Because the value
1
2
likely that
1
=
2
. We should conclude that there is a di±erence in the two
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 Spring '08
 Cheng
 Statistics, Approximation, Equal temperament, di erence, dence interval

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