Question: During the last week of the semester, students at a certain college spend on the average 4.4 hours using the school's computer terminals with a standard deviation of 1.8 hours. For a random sample of 36 students at the college, find the probabilities that the average time spent using the computer terminal during the last week of the semester is

(a) At least 4.8 hours;
(b) Between 4.1 and 4.5 hours.