Quiz 8 Solutions
Course: Stat 231
Term: Spring 2010
Instructor: Dr. Jock MacKay
Prepared by: Murshid Kuttihassan
1. A unit is
Answer: B: a private well in Waterloo region
A unit is a single member of a set of entities being studied.
Each unit contributes a random variable.
Here
the random variable is the level of Sodium (Na) in the water.
2. The parameter
μ
represents
Answer: C: the current average Na level in previously tested private wells in the Region of Waterloo
Each
Y
i
represents the current Na level in one of the 25 previously tested private wells in the Region of Waterloo.
Y
i
=
μ
+
R
i
E
[
Y
i
] =
E
[
μ
] +
E
[
R
i
]
=
μ
+ 0
=
μ
3. We are interested in assessing the hypothesis
Answer: C:
μ
= 2
.
25
Since the goal is to see if the average level has changed, the hypothesis is
μ
= 2
.
25.
4. The degrees of freedom associated with ˆ
σ
are
Answer: B: 24
The sample size is 25. 1 degree of freedom is lost while estimating the mean.
5. The standard error of ˆ
μ
is (to three decimals)
Answer: 0.034
The standard error of ˆ
μ
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 Spring '10
 McKay
 Standard Deviation, Standard Error, Yi, fuel consumption

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