Exam 8: Interval Estimation

Choo Choo Paper Company produces papers of various thickness. A random sample of 256 cuts had a mean thickness of 30.3 mils with a standard deviation of 4 mils. Develop a 95% confidence interval for the mean thickness of the population.

The makers of a soft drink want to identify the average age of its consumers. A sample of 55 consumers was taken. The average age in the sample was 21 years with a standard deviation of 4 years. a. Construct a 95% confidence interval for the true average age of the consumers. b. Construct an 80% confidence interval for the true average age of the consumers. c. Discuss why the 95% and 80% confidence intervals are different.

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

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 μ

The average score of a sample of 87 senior business majors at UTC who took the Graduate Management Admission Test was 510 with a standard deviation of 36. Provide a 98% confidence interval for the mean of the population.

As the sample size increases, the margin of error

Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.8 hours. -Refer to Exhibit 8-1. With a 0.95 probability, the margin of error is approximately

When the level of confidence decreases, the margin of error

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

In order to use the normal distribution for interval estimation of μ when σ is known and the sample is very small, the population

In order to determine the average weight of carry-on luggage by passengers in airplanes, a sample of 16 pieces of carry-on luggage was weighed. The average weight was 20 pounds. Assume that we know the standard deviation of the population to be 8 pounds. a. Determine a 97% confidence interval estimate for the mean weight of the carry-on luggage. b. Determine a 95% confidence interval estimate for the mean weight of the carry-on luggage.

Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.8 hours. -Refer to Exhibit 8-1. The standard error of the mean is

Exhibit 8-6 A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. -Refer to Exhibit 8-6. If we want to determine a 95% confidence interval for the average hourly income, the value of "t" statistics is

Exhibit 8-6 A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. -Refer to Exhibit 8-6. The standard error of the mean is

After computing a confidence interval, the user believes the results are meaningless because the width of the interval is too large. Which one of the following is the best recommendation?

We are interested in conducting a study in order to determine what percentage of voters of a state would vote for the incumbent governor. What is the minimum size sample needed to estimate the population proportion with a margin of error of 0.05 or less at 95% confidence?

The t value for a 95% confidence interval estimation with 24 degrees of freedom is

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.

In a sample of 200 individuals, 120 indicated they are Democrats. Develop a 95% confidence interval for the proportion of people in the population who are Democrats.

Below you are given ages that were obtained by taking a random sample of 9 undergraduate students. Assume the population has a normal distribution. 40 42 43 39 37 39 a. What is the point estimate of μ? b. Determine the standard deviation. c. Construct a 90% confidence interval for the average age of undergraduate students. d. Construct a 99% confidence interval for the average age of undergraduate students. e. Discuss why the 99% and 90% confidence intervals are different.