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STAT 400
(Chapter 5.6)
Spring 2012
1.
The true weight of “10-pound” sacks of potatoes processed at a
certain packaging house follows a normal distribution with mean
of 10.1 pounds and standard deviation of 0.2 pounds.
a)
What is the probability that a sack weighs at least 10 pounds?
P
(
X
10
) =
2
.
0
1
.
10
10
Z
P
= P
(
Z
–
0.50
)
= 1 –
(
–
0.50
)
= 1 – 0.3085
=
0.6915
.
b)
A random sample of 9 sacks is selected.
What is the probability that
the average weight of these 9 is at least 10 pounds?
Case 2.
Z
X
σ
μ
n
.
P
(
X
10
) =
9
2
.
0
1
.
10
10
Z
P
= P
(
Z
–
1.50
)
= 1 –
(
–
1.50
)
= 1 – 0.0668
=
0.9332
.

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*Sign up*2.
A student commission wants to know the mean amount of money spent by
college students for textbooks in one semester.
Suppose the population
mean is $450 and the population standard deviation is $40.
A random
sample of 625 students is taken.
a)

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