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Exam 8: Interval Estimation

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Question 51

Multiple Choice

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An auto manufacturer wants to estimate the annual income of owners of a particular model of automobile. A random sample of 200 current owners is selected. The population standard deviation is known. Which Excel function would NOT be appropriate to use to construct a confidence interval estimate?

A) NORM.S.INV
B) COUNTIF
C) AVERAGE
D) STDEV

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Question 52

Multiple Choice

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The general form of an interval estimate of a population mean or population proportion is the _____ plus or minus the _____.

A) population mean, standard error
B) level of significance, degrees of freedom
C) point estimate, margin of error
D) planning value, confidence coefficient

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Question 53

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A reporter for a student newspaper is writing an article on the cost of off-campus housing. A sample was selected of 10 one-bedroom units within a half-mile of campus and the rents paid. The sample mean is $550 and the sample standard deviation is $60.05. Provide a 95% confidence interval estimate of the mean rent per month for the population of one-bedroom units within a half-mile of campus. Assume this population is normally distributed.

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 _____.

An estimate of a population parameter that provides an interval believed to contain the value of the parameter is known as the _____.

In determining an interval estimate of a population mean when ? is unknown, we use a t distribution with _____ degrees of freedom.

A bank manager wishes to estimate the average waiting time for customers in line for tellers. A random sample of 50 times is measured and the average waiting time is 5.7 minutes. The population standard deviation of waiting time is 2 minutes. Which Excel function would be used to construct a confidence interval estimate?

An interval estimate is used to estimate _____.

It is known that the population variance equals 484. With a .95 probability, the sample size that needs to be taken to estimate the population mean if the desired margin of error is 5 or less is

When the level of confidence increases, the confidence interval _____.

The mean of the t distribution is _____.

The t value with a 95% confidence and 24 degrees of freedom is _____.

The sample size that guarantees all estimates of proportions will meet the margin of error requirements is computed using a planning value of p equal to _____.

If we change a 95% confidence interval estimate to a 99% confidence interval estimate, we can expect the _____.

As the number of degrees of freedom for a t distribution increases, the difference between the t distribution and the standard normal distribution _____.

A random sample of 144 observations has a mean of 20, a median of 21, and a mode of 22. The population standard deviation is known to equal 4.8. The 95.44% confidence interval for the population mean is _____.

A marketing firm is developing a new television advertisement for a large discount retail chain. A sample of 30 people is shown two potential ads and asked their preference. The results for ad #1 follow. Use Excel to develop a 95% confidence interval estimate of the proportion of people in the population who will prefer ad #1. $\text { Prefer Advertis ement \# }$ $\begin{array}{llllll}\text { yes } & \text { no } & \text { no } & \text { yes } & \text { yes } & \text { no } \\\text { no } & \text { no } & \text { no } & \text { yes } & \text { no } & \text { yes } \\\text { no } & \text { no } & \text { yes } & \text { yes } & \text { yes } & \text { no } \\\text { yes } & \text { yes } & \text { no } & \text { no } & \text { no } & \text { yes } \\\text { yes } & \text { no } & \text { yes } & \text { yes } & \text { no } & \text { no }\end{array}$

In general, higher confidence levels provide _____.

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

A local university administers a comprehensive examination to the recipients of a B.S. degree in Business Administration. A sample of five examinations is selected at random and scored. The scores are shown below. Grade 56 85 65 86 93 Use Excel to determine an interval estimate for the mean of the population at a 98% confidence level. Interpret your results.