A quality-conscious disk manufacturer wishes to know the fraction of disks his company makes which are defective. Suppose a sample of 609 floppy disks is drawn. Of these disks, 536 were not defective. Using the data, estimate the proportion of disks which are defective. Enter your answer as a fraction or a decimal number rounded to three decimal places.
b. Using the data, construct the 90% confidence interval for the population proportion of disks which are defective. Round your answers to three decimal places.

A manufacturer of automobile batteries is concerned about the life of the batteries that are produced. The manufacturer is comfortable with the average life of the batteries but more concerned about the standard deviation. Research has shown that the average life of the automobile batteries is 55 months. However, the manufacturer would like the standard deviation of the life of the automobile batteries to be relatively small, say, approximately nine months. To determine a reliable range of the standard deviation of the batteries currently being produced, the manufacturer took a random sample of 20 batteries and found that the average life was 58 months with a standard deviation of eight months. Assuming that the life of batteries produced by the automobile manufacturer has an approximately normal distribution, construct an 80% confidence interval for the standard deviation of the life of their automobile batteries. Round any intermediate calculations to no less than six decimal places and round the endpoints of the interval to four decimal places.

A research company desires to know the mean consumption of meat per week among males over age 43. A sample of 1384 males over age 43 was drawn and the mean meat consumption was 3 pounds. Assume that the population standard deviation is known to be 1.3 pounds. Construct the 99% confidence interval for the mean consumption of meat among males over age 43. Round your answers to one decimal place.

An independent group of food service personnel conducted a survey on tipping practices in a large metropolitan area. They collected information on the percentage of the bill left as a tip for 40 randomly selected bills. The average tip was 12.1% of the bill with a standard deviation of 2.6%. Assume that the tips are approximately normally distributed. Construct an interval to estimate the true average tip (as a percent of the bill) with 90% confidence. Round the endpoints to two decimal places, if necessary.

Considering the following scenario, which method would be most appropriate when calculating the margin of error for the population mean?
σ is known; n=52 ; the population is normally distributed.