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STAT 409
Fall 2011
Version B
Name
ANSWERS
.
Exam 1
Page
Earned
/
70
Be sure to show all your work; your
partial credit might depend on it.
Put your final answers at the end of
your work, and mark them clearly.
No credit will be given
without supporting work.
The exam is closed book and closed notes.
You are allowed to use a calculator and
one 8½" x 11" sheet with notes.
1
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6
Total
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1.
In a random sample of
11
“
½pound” burgers at
Burger Queen
, the average weight
of beef was 7.9 ounces with the sample standard deviation 0.12 ounces.
(Assume the
weights are normally distributed.)
a)
(5)
Construct a 95% confidence interval for the overall average weight of beef in a
“
½pound” burger at
Burger Queen
.
X = 7.9.
s = 0.12.
n
= 11.
α
= 0.05.
σ
is unknown.
The confidence interval :
X
t
s
±
α
2
n
.
α
2
=
0.025.
number of degrees of freedom =
n

1 = 11

1 =
10.
t
α
2
=
2.228.
11
12
.
0
228
.
2
9
.
7
⋅
±
7.9
±
0.08
(
7.82
, 7.98
)
b)
(5)
Construct a onesided 90% confidence interval which gives an upper bound for the
overall standard deviation of the weights of beef in a “
½pound” burger at
Burger Queen
.
( )

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 Fall '11
 STEPHANOV

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