BA 240
W. Li
Answer Sheet
1
QUIZ 6 Solution
Show your work Completely
Round to the THIRD decimal place.
Interpret your results!
Problem 1
:
Suppose the average annual expense for a
random sample of 12 stock funds
is normally
distributed with mean of 1.63 percent with a standard deviation of .31 percent. Calculate
a 95 percent confidence interval for
the mean annual expense
charged by all stock
funds.
Note:
“the mean annual expense”
indicates this question is asking for
POPULATION
MEAN
;
“random sample of 12 stock funds”
indicates this is a
SMALL SAMPLE
–
therefore we should use
t test statistic
.
12
n
,
63
.
1
x
,
31
.
0
s
,
05
.
0
95
.
0
1
,
11
1
n
df
,
201
.
2
11
,
025
.
0
t
827
.
1
,
433
.
1
197
.
0
63
.
1
12
31
.
0
201
.
2
63
.
1
2
/
n
s
t
x
201
.
2
2
/
t
Lower Limit = 1.433
Upper Limit = 1.827
The 95% confidence interval for the mean annual expense charged by all stock
funds is between 1.433 percent and 1.827 percent (or 1.433% and 1.827%).
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 Spring '08
 Li
 Normal Distribution, single repair, 1.63 percent, 1.433 percent

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