Business stats ch 9 test bank Study Guide Graded A
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NU1426
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NU1426
Business stats ch. 9 test bank Study Guide Graded A+
The mean number of travel days per year for salespeople employed by three 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...
Business stats ch. 9 test bank Study Guide
Graded A+
1). The mean number of travel days per year for salespeople employed by three 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?
Ans: 133
2). A research firm needs to estimate within 3% the proportion of junior executives leaving
large manufacturing companies within three years. a 0.95 degree of confidence is to be
used. several years ago, a study revealed that 21% of junior executives left their company
within three years. to update this study, how many junior executives should be surveyed?
Ans: 709
3). There are 2,000 eligible voters in a precinct. a total of 500 voters are randomly selected and
asked whether they plan to vote for the democratic incumbent or the republican challenger.
of the 500 surveyed, 350 said they would vote for the democratic incumbent. using the 0.99
confidence coefficient, what are the confidence limits for the proportion that plan to vote for
the democratic incumbent?
Ans: 0.647 and 0.753
4). A random sample of 85 supervisors revealed that they worked an average of 6.5 years
before being promoted. the population standard deviation was 1.7 years. using the 0.95
degree of confidence, what is the confidence interval for the population mean?
Ans: 6.14 and 6.86
5). The mean weight of trucks traveling on a particular section of i-475 is not known. a state
highway inspector needs an estimate of the population mean. he selects and weighs a
random sample of 49 trucks and finds the mean weight is 15.8 tons. the population
standard deviation is 3.8 tons. what is the 95% confidence interval for the population mean?
Ans: 14.7 and 16.9
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, 6). A bank wishes to estimate the mean credit card balance owed by its customers. the
population standard deviation is estimated to be $300. if a 98% confidence interval is used
and an interval of $75 is desired, how many customers should be sampled?
Ans: 87
7). Mileage tests were conducted on a randomly selected sample of 100 newly developed
automobile tires. the results showed that the mean tread life was 50,000 miles, with a
standard deviation of 3,500 miles. what is the best estimate of the mean tread life in miles
for the entire population of these tires?
Ans: 50,000
8). What is the interpretation of a 96% confidence level?
Ans: Approximately 96 out of 100 such intervals would include the true value of the
population parameter.
9). Which statement(s) is/are correct about the t distribution?
Ans: All apply
10). What kind of distribution is the t distribution?
Ans: Continuous
11). How is the t distribution similar to the standard z distribution?
Ans: Both are continuous distributions.
12). A random sample of 20 items is selected from a population. when computing a confidence
interval for the population mean, what number of degrees of freedom should be used to
determine the appropriate t-value?
Ans: 19
13). Of the following characteristics, the t distribution and z distribution are the same in all but
one. which one is it?
Ans: Mean = 0, and standard deviation = 1
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