The cost of textbooks relative to other expenses has risen greatly over the past few years, and university officials have started to include the average amount expended on textbook in the estimated yearly expenses for students.In order for these estimates to be useful, they should be within $25 of the mean expenditure for all undergraduate students at the university. How many students should the university sample in order to build 95% confident that its estimated cost of the textbooks will satisfy the stated level of accuracy ? From the data collected in previous year the university officials have determined the annual expenditure for textbooks has normal distribution with cost ranging from $250 to $750.