If Amir ran 26.2 miles in 5 hours, then in order to find his average number of miles run in an hour, we have to divide the total distance by the time it took him to reach that distance. In this example, his total distance was 26.2 miles, and he ran it in 5 hours, so we would divide 26.2 by 5 (26.2 / 5 = 5.24), and when we do that, we get 5.24 miles per hour.
