Homework 9 Solutions
11.21
a.
9
6
31
.
2
76
±
or 71.38 to 80.62;
df =
n
−
1 =9
−
1 = 8 for
t
*
.
b.
9
6
86
.
1
76
±
or 72.28 to 79.72
c.
16
6
75
.
1
76
±
or 73.375 to 78.625;
df =
n
−
1 = 16
−
1 = 15 for
t
*
.
d.
16
8
13
.
2
76
±
or 71.74 to 80.26
e.
16
8
13
.
2
100
±
or 95.74 to 104.26
11.23
a.
2.52
b.
2.13
c.
4.60
d.
2.06
e.
1.99
11.24
a.
2
9
6
)
(
s.e.
=
=
=
n
s
x
. Roughly, this is the average difference between the
sample and population means over all random samples of
n
= 9 that can be
selected from this population.
b.
26.2
±
(2
×
2), or 22.2 to 30.2 sit-ups.
c.
With 95% confidence, we can estimate that in the population of men
represented by this sample the mean number of sit-ups in a minute is between
22.2 and 30.2.
11.31
a.
3
.
0
81
7
.
2
)
(
s.e.
=
=
=
n
s
x
inch. Approximate 95% confidence interval is
Sample estimate
±
2
×
Standard error
, which is 64.2
±
(2
×
0.3), or 63.6 to 64.8
inches.
b.

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