We have the training program designed to upgrade the teaching skills of special education teachers. Because the program is self-administered, teachers need different numbers of hours to complete the program. A study of past participation points out that the mean length of time spent on the program is 500 hours and that this is normally distributed with a standard deviation of 100 hours.
What is the probability that a candidate chosen at random will take between 420 and 570 hours to complete the program?