bus stat ch 8
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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?
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CONFIDENCE.NORM
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Exhibit 8-2 The manager of a grocery store has taken a random sample of 100 customers. The average length of time it took these 100 customers to check out was 3.0 minutes. It is known that the standard deviation of the checkout time is one minute. Refer to Exhibit 8-2. The 95% confidence interval for the average checkout time of all customers is
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2.804 to 3.196
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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 taken. The population standard deviation is known. Which Excel function would not be appropriate to use to construct a confidence interval estimate?
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COUNTIF
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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
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7.84 or less
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An interval estimate is used to estimate
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a population parameter
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If we want to provide a 95% confidence interval for the mean of a population, the confidence coefficient is
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0.95
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The t value with a 95% confidence and 24 degrees of freedom is
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2.064
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To compute the minimum sample size for an interval estimate of m, we must first determine all of the following except
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degrees of freedom
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A random sample of 25 statistics examinations was taken. The average score in the sample was 76 with a variance of 144. Assuming the scores are normally distributed, the 99% confidence interval for the population average examination score is
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69.82 to 82.18
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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
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confidence coefficient
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As the degrees of freedom increase, the t distribution approaches the
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normal distribution
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From a population that is not normally distributed and whose standard deviation is not known, a sample of 50 items is selected to develop an interval estimate for m. Which of the following statements is true?
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The t distribution with 49 degrees of freedom must be used.
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For the interval estimation of m when s is assumed known, the proper distribution to use is the
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standard normal distribution
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A 95% confidence interval for a population mean is determined to be 100 to 120. If the confidence coefficient is reduced to 0.90, the interval for m
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becomes narrower
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The ability of an interval estimate to contain the value of the population parameter is described by the
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confidence level
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Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university, data were collected from a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.2 hours. Refer to Exhibit 8-1. With a 0.95 probability, the margin of error is approximately
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0.26
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In developing an interval estimate of the population mean, if the population standard deviation is unknown
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the sample standard deviation and t distribution can be used
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From a population that is normally distributed with an unknown standard deviation, a sample of 25 elements is selected. For the interval estimation of m, the proper distribution to use is the
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t distribution with 24 degrees of freedom
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Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university, data were collected from a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.2 hours. Refer to Exhibit 8-1. If the sample mean is 9 hours, then the 95% confidence interval is approximately
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8.74 to 9.26 hours
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A sample of 26 elements from a normally distributed population is selected. The sample mean is 10 with a standard deviation of 4. The 95% confidence interval for m is
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8.384 to 11.616
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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
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.50
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Exhibit 8-2 The manager of a grocery store has taken a random sample of 100 customers. The average length of time it took these 100 customers to check out was 3.0 minutes. It is known that the standard deviation of the checkout time is one minute. Refer to Exhibit 8-2. With a .95 probability, the sample mean will provide a margin of error of
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.196
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If we change a 95% confidence interval estimate to a 99% confidence interval estimate, we can expect the
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width of the confidence interval to increase
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In determining the sample size necessary to estimate a population proportion, which of the following information is not needed
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the mean of the population
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We can use the normal distribution to make confidence interval estimates for the population proportion, p, when
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Both np ³ 5 and n(1 - p) ³ 5
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Exhibit 8-2 The manager of a grocery store has taken a random sample of 100 customers. The average length of time it took these 100 customers to check out was 3.0 minutes. It is known that the standard deviation of the checkout time is one minute. Refer to Exhibit 8-2. If the confidence coefficient is reduced to 0.80, the standard error of the mean
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remains unchanged
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The expression used to compute an interval estimate of m may depend on any of the following factors except
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whether there is sampling error
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When the level of confidence increases, the confidence interval
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becomes wider
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Exhibit 8-2 The manager of a grocery store has taken a random sample of 100 customers. The average length of time it took these 100 customers to check out was 3.0 minutes. It is known that the standard deviation of the checkout time is one minute. Refer to Exhibit 8-2. The standard error of the mean equals
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.100
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For which of the following values of p is the value of p(1 - p) maximized?
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p=.50
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As the number of degrees of freedom for a t distribution increases, the difference between the t distribution and the standard normal distribution
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becomes smaller
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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. The 86.9% confidence interval for m is
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57.735 to 62.265
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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 the sample size was 25 (other factors remain unchanged), the interval for m would
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become wider
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it is known that the population variance equals 484. With a 0.95 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
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75
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Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university, data were collected from a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.2 hours. Refer to Exhibit 8-1. The standard error of the mean is
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.133
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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?
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If the sampling procedure were repeated many times, 95% of the resulting confidence intervals would contain the population mean systolic blood pressure
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A random sample of 36 students at a community college showed an average age of 25 years. Assume the ages of all students at the college are normally distributed with a standard deviation of 1.8 years. The 98% confidence interval for the average age of all students at this college is
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24.301 to 25.699
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The confidence associated with an interval estimate is called the
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confidence level
