Exam 8: Interval Estimation

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 random sample of 81 credit sales in a department store showed an average sale of $68.00.From past data,it is known that the standard deviation of the population is $27.00. a.Determine the standard error of the mean. b.With a 0.95 probability,what can be said about the size of the margin of error? c.What is the 95% confidence interval of the population mean?

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.

If we change a 95% confidence interval estimate to a 99% confidence interval estimate,we can expect

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 0.8 seconds.Determine a 98% confidence interval for the average CPU time.

A local health center noted that in a sample of 400 patients 80 were referred to them by the local hospital. a.Provide a 95% confidence interval for all the patients who are referred to the health center by the hospital. b.What size sample would be required to estimate the proportion of hospital referrals with a margin of error of 0.04 or less at 95% confidence?

The z value for a 97.8% confidence interval estimation is

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.

A new brand of chocolate bar is being market tested.Four hundred of the new chocolate bars were given to consumers to try.The consumers were asked whether they liked or disliked the chocolate bar.You are given their responses below. a.What is the point estimate for the proportion of people who liked the chocolate bar? b.Construct a 95% confidence interval for the true proportion of people who liked the chocolate bar. c.With a .95 probability,how large of a sample needs to be taken to provide a margin of error of 3% or less?

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 "t" value for this interval estimation is

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.

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.The standard error of the mean is

Which of the following best describes the form of the sampling distribution of the sample proportion?

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

For which of the following values of P is the value of P(1 - P)maximized?

Whenever using the t distribution for interval estimation (when the sample size is very small),we must assume that

A statistician employed by a consumer testing organization reports that at 95% confidence he has determined that the true average content of the Uncola soft drinks is between 11.7 to 12.3 ounces.He further reports that his sample revealed an average content of 12 ounces,but he forgot to report the size of the sample he had selected.Assuming the standard deviation of the population is 1.28,determine the size of the sample.

The Highway Safety Department wants to study the driving habits of individuals.A sample of 121 cars traveling on the highway revealed an average speed of 60 miles per hour with a standard deviation of 11 miles per hour.Determine a 95% confidence interval estimate for the speed of all cars.

In interval estimation,the t distribution is applicable only when

In a sample of 400 voters,360 indicated they favor the incumbent governor.The 95% confidence interval of voters not favoring the incumbent is