We would like to estimate the true mean amount of money spent on textbooks by U of M students in one semester. Suppose that textbook costs are known to follow a normal distribution with standard deviation $111. We take a random sample of 23 students and calculate a mean cost of $365.
(a) Find the margin of error for a 89% confidence interval for the true mean cost of textbooks of U of M students in one semester.
(b) The 89% confidence interval for the true mean cost of textbooks for one semester is?