20. How does the speed of a runner vary over the course of a marathon (a distance of 42.195 km)? Consider determining both the time to run the rst 5 kmand the time to run between the 35-km and 40-km points, and then subtracting the former time from the latter time.

A positive value of this difference corresponds to a runner slowing down toward the end of the race. The accompanying histogram is based on times of runners who participated in several different Japanese marathons ( Factors Affecting Runners Marathon Performance, Chance, Fall 1993: 24—30).

What are some interesting features of this histogram?

What is a typical difference value? Roughly what proportion of the runners ran the late distance more quickly than the early distance?