Exam 7: Confidence Intervals and Sample Size

A study of 60 white mice showed that their average weight was 5.7 ounces.The standard deviation of the population is 0.4 ounces.Which of the following is the 90% confidence interval for the mean weight per White mouse?

Noting that the critical z-value for a 95% confidence interval for a proportion is almost equal to 2, it can be seen that the required sample size is approximately equal to the reciprocal of the squared desired margin of error.

Jennifer wants to find a 95% confidence interval for the time it takes her to get to work.She kept records for 30 days and found her average time to commute to work was 20.5 minutes with a standard deviation of 3.9 minutes.Jennifer's maximum error of estimate would be 1.4 minutes.

The Academy of Orthopedic Surgeons states that 80% of women wear shoes that are too small for their feet.A researcher wants to be 98% confident that this proportion is within 3% of the true proportion. How large a sample is necessary?

A study of 60 professors showed that the time they spent on the average in creating test questions was 17.0 minutes per question.The standard deviation of the population is 2.Which of the following is the 98% confidence interval for the average number of minutes it takes to create a test question?

A sample of 25 different payroll departments found that the employees worked an average of 310.3 days a year.Assume a population standard deviation of 23.8 days.What is the 90% confidence interval for the Average days worked, μ, of all payroll departments?

In a sample of 855 bartenders, 48% heard complaints from patrons about work.If the margin of error was 4.4%, what was the confidence level that was used?

A recent study of 750 Internet users in Europe found that 35% of Internet users were women.What is the 95% confidence interval of the true proportion of women in Europe who use the Internet?

The rounding rule for a confidence interval for a proportion is to round off to three decimal places.

In a sample of 50 mice, a biologist found that 38% were able to run a maze in 30 seconds or less.Find the 95% limit for the population proportion of mice who can run that maze in 30 seconds or less.

According to Statistics Canada, on July 1, 2006 the population size of the province of Quebec was 7,651,531 whereas Nova Scotia was considerably smaller at 934,405.Thus the margin of error for a Gallup Poll based on a random sample of 1000 Nova Scotians is smaller than that based on a random sample of 1000 Quebeckers.

If is equal to 0.76, then is equal to

A study of 90 bolts of carpet showed that their average length was 180 yards.The standard deviation of the population is 10 yards.Which of the following is the 99% confidence interval for the mean length per Bolt of carpet?

The t-distribution has a variance that is greater than one.

A quality control expert wants to estimate the proportion of defective components that are being manufactured by his company to within 2.5%.A sample of 300 components showed that 20 were defective.How large a sample is needed to estimate the true proportion of defective components with 99% confidence? (Using the text z-table value)

Which value of was used in the figure below?

If a population has standard deviation 18, what is the minimum sample size to be 95% confident that the error should be accurate to within 4?

The confidence level of an interval estimate of a parameter is the probability that the interval estimator will contain the parameter.

A study of elephants wishes to determine the average weight of a certain subspecies of elephants.The standard deviation of the population is 2000 pounds.How many elephants need to be weighed so find we Can be 80% confident to be accurate within 300 pounds?

The value of used in the figure below is 0.025.