3. A production process is checked periodically by a quality control inspector. The inspector selects simple random samples of 30 finished products and computes the sample mean product weights . If test results over a long period of time show that 5% of the values are over 2.1 pounds and 5% are under 1.9 pounds, what are the mean and the standard deviation for the population of products produced with this process? (6 pts)

4. The Wall Street Journal reported that automobile crashes cost the United States $162 billion annually (The Wall Street Journal, March 5, 2008). The average cost per person for crashes in the Tampa, Florida, area was reported to be $1599. Suppose this average cost was based on a sample of 50 persons who had been involved in car crashes and that the population standard deviation is = $600.

4a. What is the margin of error for a 95% confidence interval? What is the 95% confidence interval? (3 pts)

4b. What would you recommend in terms of sample size if the study required a margin of error of $150 or less? Use 95% as the confidence interval. (3 pts)

4c. Calculate the 99% and 90% confidence intervals for n = 50. Comment on the differences among the three confidence intervals with different confidence coefficients. (7 pts)