AS Exercise 1 (10 marks) One step in the manufacture of a certain metal clamp involves the drilling of four holes. In a sample of 150 clamps, the average time needed to complete this step was 72 seconds and the variance was 100 seconds. (a) Find an 87% confidence interval for the mean time needed to complete the step. (b) What is the confidence level of the interval (69, 75)? (c) (d) How many clamps must be sampled so that the width of a 93.5% confidence interval is 3? Find a 96% upper confidence bound for the mean time to complete the step.