Exam 7: Confidence Intervals and Sample Size

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

The prices (in dollars) for a graphing calculator are shown below for 8 online vendors. Estimate the population standard deviation in price with 90% confidence.

In a sample of 855 bartenders, 48.0% report hearing complaints from patrons about their jobs. If the margin of error for the proportion of bartenders hearing job complaints is 4.4 percentage points, what is the degree of confidence used?

A study of 50 white mice showed that their average weight was 4.2 ounces. The standard deviation of the population is 0.7 ounces. Which of the following is the 90% confidence interval for the mean weight per white mouse?

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?

Find the 95% confidence interval for the variance of the heights of maple trees if a sample of 11 trees has a standard deviation of 12.2 feet.

In a study of 100 new cars, 30 are white. Find and , where is the proportion of new cars that are white.

The average number of mosquitos caught in 81 mosquito traps in a particular environment was 900 per trap. The standard deviation of mosquitos caught in the entire population of traps is 150 mosquitos. What is the 99% confidence interval for the true mean number of mosquitos caught in all mosquito traps?

A quality control expert wants to estimate the proportion of defective components that are being manufactured by his company. A sample of 300 components showed that 20 were defective. How large a sample is needed to estimate the true proportion of defective components to within 2.5 percentage points with 99% confidence?

Identify the degree of confidence displayed in the confidence interval shown below.

What is the value for for a 95% confidence interval when n = 18?

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

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 report states that 40% of home owners had a vegetable garden. How large a sample is needed to estimate the true proportion of home owners who have vegetable gardens to within 3% with 99% confidence?

If is equal to 0.85, then is equal to ______.

3 squirrels were found to have an average weight of 9.3 ounces with a sample standard deviation is 1.1. Find the 95% confidence interval of the true mean weight.

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

The t-distribution must be used when the sample size is greater than 30 and the variable is normally or approximately normally distributed.

A study of 65 bolts of carpet showed that their average length was 76.2 yards. The standard deviation of the population is 2.6 yards. Which of the following is the 80% confidence interval for the mean length per bolt of carpet?

A random sample of 70 printers discovered that 25 of them were being used in small businesses . Find the 95% limit for the population proportion of printers that are used in small businesses.