Quiz Review
1. The mean number of travel days per year for
salespeople employed by hardware distributors needs to
be estimated with a 0.90 degree of confidence. For a small
pilot study the mean was 150 days and the standard
deviation was 14 days. If the population mean is estimated
within two days, how many salespeople should be
sampled?
A: 134
B: 452
C: 511
D: 2100
2. A random sample of 85 group leaders, supervisors, and
similar personnel revealed that a person spent an average
6.5 years on the job before being promoted. The standard
deviation of the sample was 1.7 years. Using the 0.95
degree of confidence, what is the confidence interval for
the population mean?
A: 6.99 and 7.99
B: 4.15 and 7.15
C: 6.14 and 6.86
D: 6.49 and 7.49
3. The mean weight of trucks traveling on a particular
section of I475 is not known. A state highway inspector
needs an estimate of the mean. He selects a random
sample of 49 trucks passing the weighing station and finds
the mean is 15.8 tons, with a standard deviation of the
sample of 3.8 tons. What is the 95 percent interval for the
population mean?
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 Spring '10
 BARCUS
 Statistics, Standard Deviation, Confidence

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