A university professor who is correcting 600 written examinations decides to get a prelim- inary idea of the passing rate on the test. He decides to select a sample of exam copies as follows: She tosses an ordinary sixsided die, one for each exam copy. If the diq shows a 6, she corrects the corresponding exam, otherwise not. Suppose that the selected sample consists of 90 students and that 60 out of these are found to have passed: (a) What sampling design did the professor use? (b) Give a point estimate of the proportion of students who have passed. (c) Construct an 95% condence interval for the proportion of students who have passed