A Statistical Tutorial Centre has been designed to handle a maximum of 25 students per day. Suppose that the number X of students visiting this centre each day is a normal random variable with mean 15 and variance 16.
Part a) What is the return period for this centre rounded to the nearest day?
Part b) What is the probability that the "design" number of visits will not be exceeded before the 10th day? Leave your answer in 3 decimal places.