Assign 15. The following represent the running times of films (in minutes) produced by a certain motion picture company: 103, 97, 110, 100, 98, 99, 110, 101, 105, and 104. Assume that the running times of films produced by the company are approximately normally distributed. Find a 95% confidence interval estimate of the true population variance. Assign 16. Students may choose between a 3-unit course in Physics without lab and a 4-unit course with lab. The final written exam is the same for each section. The mean score of a random sample of 15 students in the section with lab is 84 with a standard deviation of 4, and the mean score of another random sample of 12 students in the section without lab is 77 with a standard deviation of 6. Find a 95% confidence interval for the difference between the mean grades for the two courses. Assume the populations to be approximately normally distributed with equal variances