STAT 420
Fall 2010
Homework #1
(10 points)
(due Friday, September 3, by 3:00 p.m.)
1.
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.
2.
3.12
Redo Problem 3.5
without
assuming that the population standard deviation is
known.
You are given
s
= $1,575.
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3.
A coffee machine is regulated so that the amount of coffee dispensed is normally
distributed.
A random sample of 17 cups had an average of 7.91 ounces per cup and
a sample standard deviation of 0.175 ounces.
a)
Construct a 90% confidence interval for the overall average amount of coffee
dispensed by the machine.
b)
The coffee machine manufacturer claims that the overall average amount of coffee
dispensed is at least 8 ounces.
Find the Pvalue of the test
H
0
:
μ
= 8
vs.
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 Spring '08
 Stepanov
 Statistics, Standard Deviation, researcher, University of Wisconsin, transit system

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