STP 226, Spring 2021 Final Exam Study Guide 28. A medication for blood pressure was administered to a group of 13 randomly selected patients with elevated blood pressures while a group of 15 was given a placebo. At the end of three months, the following data was obtained on their systolic blood pressure. The placebo group had a mean blood pressure of 180 mmig with a standard deviation of 50 mmig, while the treatment group had a mean blood pressure of 150 mmig and a standard deviation of 30 mmHg. Find and briefly interpret the 95% confidence interval for the difference between the mean blood pressure of the placebo group minus the treatment group. 29. It is believed that the length, in minutes, of theatrically released movies has been getting shorter throughout the years. Prior to 1980, [suppose] the average length of successful films in the box office was 125 minutes. From a random sample of 38 successful films in the box office, it was found that they had an average length of 120.9 minutes with a standard deviation of 8.7 minutes. With a 1% level of significance, test the claim that the true average length of films released in theaters is less than the old average of 125 minutes. a. State the hypotheses Ho and H1. b. Calculate the appropriate test statistic. . Find the critical value and the rejection region. d. What is the decision of this test? e. Briefly interpret the decision of this test. 30. A manufacturing plant that makes gizmos wants to know the proportion of gizmos that are defective. A sample of 612 yielded 45 defected gizmos. Based on this sample, construct and interpret a 95% confidence interval for the true proportion of defective gizmos