Exam 7: Confidence Intervals and Sample Size

The average score for 49 teenage boys playing a certain computer game was 80,000 points per player. If the standard deviation of the population is 20,000 points, find the 95% confidence interval of the mean score for all teenage boys.

The value of used in the figure below is 0.02.

A 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 80% confidence interval for the average weight of a nickel. How many nickels does he need to weigh to obtain an average accurate to within 10 milligrams?

A report states that 44% of home owners have a vegetable garden. How large a sample is needed to estimate the true proportion of home owners who have vegetable gardens to within 3 percentage points with 92% confidence?

What is the value for for a 98% confidence interval when n = 12?

The value for for a 95% confidence interval when n = 15 is 26.119.

A sample of 35 different payroll departments found that employees worked an average of 240.6 days a year. If the population standard deviation is 18.8 days, find the 90% confidence interval for the average number of days worked by all employees who are paid through payroll departments.

The symbol for the sample proportion is ______.

The winning team's score in 7 high school basketball games was recorded. If the sample mean is 68.3 points and the sample standard deviation is 13.0 points, find the 98% confidence interval of the true mean.

In order to find confidence intervals for variances and standard deviations, one must assume that the variable is _________________.

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 term describes the ___________________.

What value of is used in confidence interval shown below?

A random sample of magnesium concentrations (in parts per million, or ppm) in ground water from various locations follows. Estimate the mean concentration of magnesium in ppm with 90% confidence. Assume .

The area under each chi-square distribution is equal to _______.

A student looked up the number of years served by 35 of the more than 100 Supreme Court justices. The average number of years served by those 35 justices was 13.8. If the standard deviation of the entire population is 7.3 years, find the 95% confidence interval for the average number of years served by all Supreme Court justices.

A researcher conducted a study of the access speed of 45 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 5, about how many hard drives should he include in his new sample?

A study of 45 professors showed that the average time they spent creating test questions was 15.5 minutes per question. The standard deviation of the population is 5.8. Which of the following is the 98% confidence interval for the average number of minutes it takes to create a test question?

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

John Davis, a manager of a supermarket, wants to estimate the proportion of customers who use food stamps at his store. He has no initial estimate of what the sample proportion will be. How large a sample is required to estimate the true proportion to within 3 percentage points with 98% confidence?