January 21, 2012
This example should help with your homework. We will brieﬂy talk about it in class on Monday.
An industrial plant claims to discharge no more than 1000 gallons of wastewater per hour, on the average,
into a neighborhood lake. An environmental group decides to monitor the plant, in case this limit is being
exceeded. Doing so is expensive, and only a small sample is possible. A random sample of four hours is
selected over a period of a week. The observations are: 2000, 1000, 3000, 2000. From these data we can ﬁnd
¯
x
= 2000 and
s
= 816
.
5.
Key Information
From the problem we know that
n
= 4, ¯
x
= 2000, and
s
= 816
.
5. Also, our “guess” that we’ll be evaluating
is
μ
0
= 1000.
1 Assumptions
We must ﬁrst check if the assumptions are met.
•
Data obtained by randomization? Yes
•
Quantitative response? Yes (number of gallons)
•
Population distribution is approximately normal? Maybe. If the researchers believe it is, then that’s
what we’ll go with.
2 Hypotheses
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 Spring '08
 TA
 Null hypothesis, four hours, 1000 gallons

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