Exam 8: Interval Estimation

Computer Services, Inc.wants to determine a confidence interval for the average CPU time of their teleprocessing transactions.A sample of 64 transactions yielded a mean of 6 seconds with a standard deviation of .8 seconds.Determine a 98% confidence interval for the average CPU time of all the teleprocessing transactions.

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 an 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 true average daily sales. b. Provide a 97% confidence interval estimate for the true average daily sales.

In a random sample of 400 registered voters, 120 indicated they plan to vote for Candidate A.Determine a 95% confidence interval for the proportion of all the registered voters who will vote for Candidate A.

The average monthly electric bill of a random sample of 256 residents of a city is $111 with a standard deviation of $32. ​ a. Construct a 90% confidence interval for the mean monthly electric bills of all residents. b. Construct a 95% confidence interval for the mean monthly electric bills of all residents.

The degrees of freedom associated with a t distribution are a function of the​

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.

A coal company wants to determine a 95% confidence interval estimate for the average daily tonnage of coal that they mine.Assuming that the company reports that the standard deviation of daily output is 200 tons, how many days should they sample so that the margin of error will be 39.2 tons or less?

As the sample size increases, the margin of error

It is known that the variance of a population equals 576.A random sample of 144 observations is going to be taken from the population. a. With a .95 probability, what statement can be made about the size of the margin of error? b. With a .95 probability, how large of a sample would have to be taken to provide a margin of error of 6 or less?

In November 2018, 50,000 people living in the United States were asked whether they had a computer at home.43,128 answered yes, they had a computer at home.There were 326,766,748 people living in the United States at the time of the survey.Determine an interval with 99% confidence for the number (how many) of people living in the United States who have a computer at home.

In order to estimate the average time spent per student on the computer terminals at a local university, data were collected for a sample of 64 business students over a one-week period.Assume the population standard deviation is 1.6 hours.The standard error of the mean is

A population has a standard deviation of 25.A random sample of 125 items from this population is selected.The sample mean is determined to be 325.At 95% confidence, the margin of error is

In order to estimate the average electric usage per month, a sample of 256 houses was selected and their electric usage was determined.Assume a population standard deviation of 500 kilowatt-hours. a. Determine the standard error of the mean. b. With a .95 probability, determine the margin of error. c. If the sample mean is 2500 kWh, what is the 95% confidence interval estimate of the population mean?

A random sample of 25,000 ACT test takers had an average score of 21 with a standard deviation of 5.What is the 95% confidence interval of the population mean?

​The margin of error in an interval estimate of the population mean is a function of all of the following except

Confidence intervals for the population mean µ and population proportion p _____ as the size of the sample increases.

To compute the minimum sample size for an interval estimate of μ, we must first determine all of the following except

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

A sample of 200 commuters in Boston indicated that they commute an average of one hour and fifteen minutes per day.The standard deviation of the sample was 25 minutes.Compute the 95% confidence interval for the average commute time of the population (in minutes).

A sample of 100 students from a large university was taken.The average age in the sample was 22 years with a standard deviation of 4 years.Construct a 95% confidence interval for the average age of the population.