On an uphill hike, Ted climbs at a rate of 3 miles an hour. Going down, he runs at a rate of 5 miles an hour. If it takes him 40 minutes longer to climb up than run down, what is the total length of Ted's hike?

It takes 40 minutes more going up or 40/60 = 0.67 hours more.

Let us say that:

t = the time required for him running down

t + 0.67 = time required for him running up

Since the distance of running up and down must be equal therefore:

(3 miles / hr) * (t + 0.67) = (5 miles / h) * t

3 t + 2.01 = 5 t

2 t = 2.01

t = 1.005 hr

So the total length of the hike is:

length = 2 * (5 miles / hr) * (1.005 hr)

length = 10.05 miles