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Answer Key for Exam 1 ( Version D)
1. The hypothesized mean time (= 8) is not included in the confidence interval ( 8.3 to 9.4 ). The
decision is to reject Ho and conclude there is evidence the average warmup period is not equal to
8 minutes.
NOTE
: 90% C.I. is related to a twotailed test at the 10% significant level.
Ans. D
2. A Type I error occurs if you reject Ho when in fact it is true (see page 273).
In this case, Ho
states “the average warmup time is equal to 8 minutes.”
So rejecting Ho is concluding the mean
is not equal to 8 minutes.
Ans. E
3. From the given Excel output, the absolute value of T* (=t stat.) is = 2.0718
Ans. C
4. From the given Excel output, pvalue ( =.0286) > α (=.01). The decision is to fail to reject Ho.
Conclude there is insufficient evidence the annual utility expenses are more than $25,000.
Ans. A
5. The required C. I. is given by (
) ±
t
α / 2, df
* √(S
2
/ n ).
Using α/2 = .01/2 = .005
and df = 14, we
have .t
α / 2, df
= 2.977 from ttable. From the Excel output we have (26129.13)
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 Spring '08
 Dr.Jay

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