The amounts of time per workout an athlete uses a stairclimber are normally distributed, with a mean of 21 minutes and a standard deviation of 5 minutes. Find the probability that a randomly selected athlete uses a stairclimber for (a) less than 16 minutes, (b) between 21 and 28 minutes, and (c) more than 30 minutes (a) The probability that a randomly selected athlete uses a stairclimber for less than 16 minutes is (Round to four decimal places as needed.)