Exam 7: Confidence Intervals and Sample Size

For a random sample of 23 European countries, the variance on life expectancy was 7.3 years. What is the 95% confidence interval for the variance of life expectancy in all of Europe?

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

Find the values for and when = .05 and n = 27.

Find the 95% confidence interval for the standard deviation of the lengths of pipes if a sample of 11 pipes has a standard deviation of 14.6 inches.

In a study using 8 samples, and in which the population variance is unknown, the distribution that should be used to calculate confidence intervals is

When computing a confidence interval for a population mean using raw data, round off to two more decimal places than the number of decimal places in the original data.

An interval estimate may or may not contain the true value of the parameter being estimated.

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 percentage points of the true proportion. How large a sample is necessary?

A study of elephants is conducted to determine the average weight of a certain subspecies of elephants. The standard deviation for the population is 1500 pounds. At a 95% level, how many elephants need to be weighed so the average weight will be accurate to within 250 pounds?

According to a study of 90 truckers, a trucker drives, on average, 540 miles per day. If the standard deviation of the miles driven per day for the population of truckers is 40, find the 99% confidence interval of the mean number of miles driven per day by all truckers.

What is the 90% confidence interval for the variance of exam scores for 28 algebra students, if the standard deviation of their last exam was 12.7?

A recent poll of 700 people who work indoors found that 278 smoke. If the researchers want to be 98% confident of their results to within 3.5 percentage points, how large a sample is necessary?

The _________________ are the number of values that are free to vary after a sample statistic has been computed.

A sample of 400 racing cars showed that 80 of them cost over $700,000. What is the 99% confidence interval for the true proportion of racing cars that cost over $700,000?

A chi-square variable cannot be negative, and the distributions are positively skewed.

In a sample of 40 mice, a biologist found that 42% were able to run a maze in 30 seconds or less. Find the 90% limit for the population proportion of mice who can run a maze in 30 seconds or less.

The Pizza Shop wanted to determine what proportion of its customers ordered only cheese pizza. Out of 80 customers surveyed, 15 ordered only cheese pizza. What is the 99% confidence interval of the true proportion of customers who order only cheese pizza?

An economics professor randomly selected 100 millionaires in the United States. The average age of these millionaires was 54.8 years. If the standard deviation of the entire population of millionaires is 7.9 years, find the 95% confidence interval for the mean age of all United States millionaires.

A food snack manufacturer samples 7 bags of pretzels off the assembly line and weighs their contents. If the sample mean is 14.2 oz. and the sample standard deviation is 0.60 oz., find the 95% confidence interval of the true mean.

Find when n = 23 for the 99% confidence interval for the mean.