For an exercise study, a large group of male distance runners walk on a treadmill for five minutes. The average heart rate following the exercise is 117.6 beats per minute with standard deviation 8.1....

For an exercise study, a large group of male distance runners walk on a treadmill for five minutes. The average heart rate following the exercise is 117.6 beats per minute with standard deviation 8.1. If a sample of 43 of these runners is taken, what is the probability that their average heart rate is under 115.8 beats per minute.