Statistics (Sections 9.1 - 11.1)

Solve the problem.
7) In order to set rates, an insurance company is trying to estimate the number of sick days
that full time workers at an auto repair shop take per year. A previous study indicated
that the standard deviation was 2.1 days. a) How large a sample must be selected if the
company wants to be 90% confident that the true mean differs from the sample mean by
no more than 1 day b) Repeat part (a) using a 95% confidence interval. Which level of
confidence requires a larger sample size Explain.
7)
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
Find the specified t-value.
8) For a t-curve with df = 4, find t 0.05
.
8)
A) 1.645 B) 2.353 C) 2.132 D) 4.604
Solve the problem.
9) Find the critical t-value used for a confidence interval of the mean with a confidence level of 99%
and n = 10.
9)
A) 3.250 B) 2.2821 C) 1.833 D) 2.262
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
10) Find the critical t-value that corresponds to c = 0.95 and n = 16. (Note; confidence level
written as a decimal = c. So c = 0.95 is the 95% confidence level.)
10)
Find the confidence interval specified.
11) A sociologist develops a test to measure attitudes about public transportation, and 27
randomly selected subjects are given the test. Assume that the population is normally
distributed. The mean score of the sample is 76.2 and the sample standard deviation is
21.4. Construct the 95% confidence interval for the mean score of all such subjects.
11)
12) Construct a 95% confidence interval for the population mean, μ. Assume the population
has a normal distribution. A random sample of 16 fluorescent light bulbs has a mean life of
645 hours with a standard deviation of 31 hours.
12)
Solve the problem.
13) A survey of 250 households showed 19 owned at least one gun. Find a point estimate for
p, the population proportion of households that own at least one gun.
13)
14) In a survey of 10 golfers, 2 were found to be left-handed. Is it practical to construct the
90% confidence interval for the population proportion, p Explain.
14)
15) Many people think that a national lobbyʹs successful fight against gun control legislation is
reflecting the will of a minority of Americans. A random sample of 4000 citizens yielded
2250 who are in favor of gun control legislation. Estimate the true proportion of all
Americans who are in favor of gun control legislation using a 95% confidence interval.
15)
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