STAT 420
Fall 2008
Homework #1
(10 points)
(due Friday, September 5, by 3:00 p.m.)
From the textbook:
3.5
The salary of junior executives in a large retailing firm is normally distributed with
standard deviation
σ
= $1,500. If a random sample of 25 junior executives yields
an average salary of $16,400, what is the 95percent confidence interval for
μ
, the
average salary of all junior executives.
3.12
Redo Problem 3.5
without
assuming that the population standard deviation is
known. You are given
s
= $1,575.
3.18 (
a
), (
b
)
A cereal packaging machine is supposed to turn out boxes that contain 20 oz of
cereal on the average. Past experience indicates that the standard deviation of the
content weights of the packages turned out by the machine is
σ
= 0.25 oz. Boxes
containing less than 19.8 oz of cereal, on the average, are considered unacceptable.
Thus the manufacturer wishes to test
H
0
:
μ
= 20 and
H
a
:
μ
= 19.8.
Hint:
Treat this problem as a lefttailed test since 19.8 < 20.
a)
If samples of size
n
= 20 are drawn from the current production to test the
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 Spring '10
 Stepanov
 Statistics, Normal Distribution, Standard Deviation, transit system

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