Answer:
According to the University of Iowa, the average length of a stride is 5ft.
Now, the total distance of the marathon is:
26mi and 385yd.
Let's transform that distance into ft.
1mi = 5280ft
Then:
26mi = 26*5280ft = 137,280ft
1yd = 3ft
then:
385yd = 385*3ft = 1,155ft.
Then the total distance of the marathon, in ft, is:
D = 137,280ft + 1,155ft = 138,435 ft.
Now the average number of strides needed will be equal to the quotient between the total distance of the marathon and the distance traveled in each stride.
N = 138,435ft/5ft = 27,687.