The healing time for a certain type of incision is normally distributed with a mean of 240 hours and a standard deviation of 20 hours
a) What is he probability that the healing time for a randomly selected patient will exceed 255 hrs?
b) What is the probability that the healing time for a randomly selected patient will be exactly 240 hours
c) 90% of persons with this type of incision will require less than what amount of time to heal?