Exam 7: Confidence Intervals and Sample Size

What is the 95% confidence interval for the standard deviation of birth weights at Guelph General Hospital, if the standard deviation of the last 25 babies born there was 1.1 pounds?

A retailer wants to estimate with 99% confidence the number of people who buy at his store.A previous study showed that 24% of those interviewed had shopped at his store.He wishes to be accurate within 3% of the true proportion.The minimum sample size necessary would be 1,100.

In 2000 there were almost 300,000 Canadians with more than 1 million dollars in financial assets! If the average age of one hundred randomly selected millionaires was 54.8 years with a standard deviation of 7.9 years, what is the 95% confidence interval for the mean age, μ, of all Canadian millionaires?

Find the 95% confidence interval for the variance of the heights of maple trees if a sample of 12 trees has a standard deviation of 10 feet.

The term refers to the

A random sample of 80 voters found that 46% were going to vote for a certain candidate.Find the 95% limit for the population proportion of voters who will vote for that candidate.

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

It was found that in a sample of 90 teenage boys, 70% of them have received speeding tickets.What is the 90% confidence interval of the true proportion of teenage boys who have received speeding tickets?

A survey of 800 women shoppers found that 17% of them shop on impulse.What is the 98% confidence interval for the true proportion of women shoppers who shop on impulse?

A researcher conducted a study of the access speed of 30 hard drives and concluded that his maximum error of estimate was 20.If he were to conduct a second study to reduce the maximum error of estimate to 4, about how many hard drives should he include in his new sample?

Only the degree of confidence and the maximum error are necessary to determine the sample size if one uses the "conservative" value for the standard error.

A sample of 23 European countries found that the variance on life expectancy was 7.3 years.What is the 95% confidence interval for the variance of life expectancy in Europe?

A previous study of nickels showed that the the standard deviation of the weight of nickels is 150 milligrams.A coin counter manufacturer wishes to find the 99% confidence interval for the average Weight of a nickel.How many nickels does he need to weigh to be accurate within 15 milligrams?

The __________ is the maximum likely difference between the point estimate of a parameter and the actual value of the parameter.

Find the value of  as shown in the figure below.

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

The symbol for the sample proportion is __________. ________________________________________

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

The (estimated) standard error of the mean is larger than the standard deviation of the sample from which it was derived.

Find the 95% confidence interval for the variance of the lengths of pipes if a sample of 16 pipes has a standard deviation of 12 inches.