Question 4 [25] The amount of time devoted to preparing for a statistics examination by students is a normally distributed random variable with a mean of 17 hours and a standard deviation of 5 hours. Required: a) What is the amount of time below which only 15% of all students spend studying? b) What is the amount of time above which only one third of all students spend studying? c) What is the probability that a student spends between 16 and 20 hours studying? d) What is the probability that a student spends at least 15 hours studying? e) What is the probability that a student spends at most 18 hours studying?