Exam 7: Confidence Intervals and Sample Size

A study of peach trees found that the average number of peaches per tree was 525. The standard deviation of the population is 105 peaches per tree. A scientist wishes to find the 80% confidence interval for the mean number of peaches per tree. How many trees does she need to sample to obtain an average accurate to within 12 peaches per tree?

A college believes that 22% of applicants to that school have parents who have remarried. How large a sample is needed to estimate the true proportion of students who have parents who have remarried to within 5 percentage points with 99% confidence?

The value for for a 99% confidence interval when n = 24 is 9.262.

What is the value of $\alpha$ used in describing the confidence interval shown below.

A retailer wants to estimate with 99% confidence the number of people who shop 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.

A random sample of 100 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.

If a population has a standard deviation of 16, what is the minimum number of samples that need to be averaged in order to be 95% confident that the average of the means is within 3 of the true mean?

A previous analysis of paper boxes showed that the the standard deviation of their lengths is 15 millimeters. A packer wishes to find the 90% confidence interval for the average length of a box. How many boxes does he need to measure to be accurate within 3 millimeters?

One of the characteristics of the t-distribution is that the curve never touches the ____-axis.

A chi-square distribution is negatively skewed.

The formula for the confidence interval for a standard deviation is ____________________.

A study of 75 apple trees showed that the average number of apples per tree was 925. The standard deviation of the population is 100. Which of the following is the 95% confidence interval for the mean number of apples per tree for all trees?

The formula for the confidence interval of the mean for a specific is ____________________.

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 for the population of 3.9 minutes. Jennifer's margin of error would be 1.4 minutes.

The prices (in dollars) for a graphing calculator are shown below for 8 online vendors. Estimate the true mean price for this particular calculator with 95% confidence.