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Exam 8: Interval Estimation

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Question 1

Multiple Choice

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The following random sample from a population whose values were normally distributed was collected. The 95% confidence interval for $\mu$ is

A) 8.52 to 10.98
B) 7.75 to 12.25
C) 9.75 to 10.75
D) 8.00 to 10.00

E) B) and D)
F) B) and C)

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Question 2

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Exhibit 8-3 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 population of checkout times is one minute. -Refer to Exhibit 8-3. The 95% confidence interval for the true average checkout time (in minutes) is

A) 3:00 to 5:00
B) 1.36 to 4.64
C) 1.00 to 5.00
D) 2.804 to 3.196

E) None of the above
F) C) and D)

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Question 3

Multiple Choice

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In a random sample of 100 observations, = 0.2. The 95.44% confidence interval for P is

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. a.Compute the sample mean and the standard deviation. b.Determine the margin of error at 95% confidence. c.At 95% confidence, determine an interval for the mean of the population. At 98% confidence, determine an interval for the mean of the population.

If an interval estimate is said to be constructed at the 90% confidence level, the confidence coefficient would be

A random sample of 1000 people was taken. Four hundred fifty of the people in the sample favored Candidate A. The 95% confidence interval for the true proportion of people who favors Candidate A is

The absolute value of the difference between the point estimate and the population parameter it estimates is

Information regarding the price of a roll of camera film (35 mm, 24 exposure) for a sample of 12 cities worldwide is shown below. Determine a 95% confidence interval for the population mean.

A sample of 36 patients in a doctor's office showed that they had to wait an average of 45 minutes with a standard deviation of 10 minutes before they could see the doctor. Provide a 90% confidence interval estimate for the average waiting time of all the patients who visit this doctor.

In a poll of 600 voters in a campaign to eliminate non-returnable beverage containers, 210 of the voters were opposed. Develop a 92% confidence interval estimate for the proportion of all the voters who opposed the container control bill.

Exhibit 8-5 A random sample of 64 SAT scores of students applying for merit scholarships showed an average of 1400 with a standard deviation of 240. -Refer to Exhibit 8-5. The 95% confidence interval for the SAT scores is

A sample of 225 elements from a population with a standard deviation of 75 is selected. The sample mean is 180. The 95% confidence interval for $\mu$ is

Exhibit 8-5 A random sample of 64 SAT scores of students applying for merit scholarships showed an average of 1400 with a standard deviation of 240. -Refer to Exhibit 8-5. The margin of error at 95% confidence is

Exhibit 8-3 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 population of checkout times is one minute. -Refer to Exhibit 8-3. The standard error of the mean equals

Exhibit 8-2 A random sample of 121 automobiles traveling on an interstate showed an average speed of 65 mph. From past information, it is known that the standard deviation of the population is 22 mph. -Refer to Exhibit 8-2. If the confidence coefficient is reduced to 0.9, the standard error of the mean

In determining the sample size necessary to estimate a population proportion, which of the following information is not needed?

The z value for a 97.8% confidence interval estimation is

Exhibit 8-4 In order to estimate the average electric usage per month, a sample of 81 houses was selected, and the electric usage was determined. Assume a population standard deviation of 450-kilowatt hours. -Refer to Exhibit 8-4. At 95% confidence, the size of the margin of error is

A local electronics firm wants to determine their average daily sales (in dollars.) A sample of the sales for 36 days revealed average sales of $139,000. Assume that the standard deviation of the population is known to be $12,000. a.Provide a 95% confidence interval estimate for the average daily sales. b.Provide a 97% confidence interval estimate for the average daily sales.

It is known that the variance of a population equals 1296. A random sample of 144 observations is going to be taken from the population. a.With a 0.95 probability, what statement can be made about the size of the margin of error? b.With a 0.95 probability, how large of a sample would have to be taken to provide a margin of error of 6 or less?