Exam 8: Interval Estimation

An interval estimate is a range of values used to estimate

In order to determine the average weight of carry-on luggage by passengers in airplanes,a sample of 25 pieces of carry-on luggage was collected and weighed.The average weight was 18 pounds.Assume that we know the standard deviation of the population to be 7.5 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.

A simple random sample of 144 items resulted in a sample mean of 1257.85 and a standard deviation of 480.Develop a 95% confidence interval for the population mean.

A random sample of 64 students at a university showed an average age of 25 years and a sample standard deviation of 2 years.The 98% confidence interval for the true average age of all students in the university is

In a random sample of 400 residents of Chattanooga,320 residents indicated that they voted for the Democratic candidate in the last presidential election.Develop a 95% confidence interval estimate for the proportion of all Chattanooga residents who voted for the Democratic candidate.

In developing an interval estimate,if the population standard deviation is unknown

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.

As the sample size increases,the margin of error

In general,higher confidence levels provide

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

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 small stock brokerage firm wants to determine the average daily sales (in dollars)of stocks to their clients.A sample of the sales for 36 days revealed average daily sales of $200,000.Assume that the standard deviation of the population is known to be $18,000. a.Provide a 95% confidence interval estimate for the average daily sale. b.Provide a 97% confidence interval estimate for the average daily sale.

The ability of an interval estimate to contain the value of the population parameter is described by the

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.

A statistician selected a sample of 16 accounts receivable and determined the mean of the sample to be $5,000 with a standard deviation of $400.He reported that the sample information indicated the mean of the population ranges from $4,739.80 to $5,260.20.He neglected to report what confidence coefficient he had used.Based on the above information,determine the confidence coefficient that was used.Assume the population has a normal distribution.

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

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

A quality control technician is checking the weights of a product.She takes a random sample of 8 units and weighs each unit.The observed weights are shown below.Assume the population has a normal distribution. Provide a 95% confidence interval for the mean weight of the units.

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

The Highway Safety Department wants to study the driving habits of individuals.A sample of 81 cars traveling on the highway revealed an average speed of 67 miles per hour with a standard deviation of 9 miles per hour. a.Compute the standard error of the mean. b.Determine a 99% confidence interval estimate for the speed of all cars.