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Exam 8: Interval Estimation

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Question 41

Multiple Choice

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The t distribution is a family of similar probability distributions, with each individual distribution depending on a parameter known as the

A) finite correction factor
B) sample size
C) degrees of freedom
D) standard deviation

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Question 42

Multiple Choice

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To estimate a population mean, the sample size needed to provide a margin of error of 2 or less with a .95 probability when the population standard deviation equals 11 is

A) 10
B) 11
C) 116
D) 117

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Question 43

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A researcher is interested in determining the average number of years employees of a company stay with the company. If past information shows a standard deviation of 7 months, what size sample should be taken so that at 95% confidence the margin of error will be 2 months or less?

Exhibit 8-3 A random sample of 81 automobiles traveling on a section of an interstate showed an average speed of 60 mph. The distribution of speeds of all cars on this section of highway is normally distributed, with a standard deviation of 13.5 mph. -Refer to Exhibit 8-3. If we are interested in determining an interval estimate for $\mu$ at 86.9% confidence, the z value to use is

A real estate agent wants to estimate the mean selling price of two-bedroom homes in a particular area. She wants to estimate the mean selling price to within $10,000 with an 89.9% level of confidence. The standard deviation of selling prices is unknown but the agent estimates that the highest selling price is $1,000,000 and the lowest is $50,000. How many homes should be sampled?

The probability that the interval estimation procedure will generate an interval that does not contain the actual value of the population parameter being estimated is the

A random sample of 25 employees of a local company has been measured. A 95% confidence interval estimate for the mean systolic blood pressure for all company employees is 123 to 139. Which of the following statements is valid?

The mean of the t distribution is

A survey of 40 students at a local college asks, "Where do you buy the majority of your books?" The responses fell into three categories: "at the campus bookstore," "on the Internet," and "other." The results follow. Use Excel to estimate the proportion of all of the college students who buy their books on the Internet.

The t distribution should be used whenever

A simple random sample of 144 items resulted in a sample mean of 1080. The population standard deviation is known to be 240. Develop a 95% confidence interval for the population mean.

As the sample size increases, the margin of error

Using an $\alpha$ = 0.04, a confidence interval for a population proportion is determined to be 0.65 to 0.75. If the level of significance is decreased, the interval for the population proportion

We can reduce the margin of error in an interval estimate of p by doing any of the following except

If we want to provide a 95% confidence interval for the mean of a population, the confidence coefficient is

It is known that the variance of a population equals 1,936. A random sample of 121 has been taken from the population. There is a .95 probability that the sample mean will provide a margin of error of

The expression used to compute an interval estimate of $\mu$ may depend on any of the following factors except

A local university administers a comprehensive examination to the recipients of a B.S. degree in Business Administration. A sample of 5 examinations is selected at random and scored. The scores are shown below. Use Excel to determine an interval estimate for the mean of the population at a 98% confidence level. Interpret your results.

An apartment complex developer is considering building apartments in College Town, but first wants to do a market study. A sample of monthly rent values ($) for studio apartments in College Town was taken. The data collected from the 70-apartment sample is presented below. (Based on past experience, the developer assumes a known value of $\sigma$ = $55 for the population standard deviation.) a. Develop a 98% confidence interval for the mean monthly rent for all studio apartments in this city. b. Suppose the apartment developer wants a 98% confidence interval estimate of the population mean with a margin of error of E = $10. How large a sample size is needed?

The average monthly electric bill of a random sample of 256 residents of a city is $90. The population standard deviation is assumed to be $24. a.Construct a 90% confidence interval for the mean monthly electric bills of all residents. b.Construct a 95% confidence interval for the mean monthly electric bills of all residents.