9.54
Faced with rising fax costs, a firm issued a guideline that transmissions of 10 pages or
more should be sent by 2day mail instead. Exceptions are allowed, but they want the
average to be 10 or below. The firm examined 35 randomly chosen fax transmissions during
the next year, yielding a sample mean of 14.44 with a standard deviation of 4.45 pages. (a)
At the .01 level of significance, is the true mean greater than 10? (b) Use Excel to find the
righttail
p
value.
A)
Null Hypothesis:
H
0
= 10 and H
1
> 10
Significance level is .01 so Z0.025 = 2.3263
Z = (x – μ) / σ
x
where σ
x
= σ / sqrt n
Z = 14.44 – 10 / (4.45 / sqrt 35)
Z = 5.903
Reject the null hypothesis if the true mean is not = to 10.
B)
Using the TDIST function in excel where x = 5.903, Deg of Freedom = 34 and Tails = 1
excel found the right tail pvalue to be .00000057579
9.56
A c
oin was flipped 60 times and came up heads 38 times. (a) At the .10 level of
significance, is the coin biased toward heads? Show your decision rule and calculations. (b)
Calculate a
p
value and interpret it.
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 Spring '10
 vitale
 Statistics, Null hypothesis, Statistical hypothesis testing, TDIST

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