Question

A sportsman can run 320 feet down a sand dune in 20 seconds. He can run 240 feet up the sand dune in 60 seconds.

How fast can the sportsman run in the sand on level​ ground?

Answer 1

320 /20 = 16' per second

240/ 60 = 4' per second

Let his speed on level ground be x ' per second

Let force of gravity be g ' per second

DOWN the sand dune = x + g = 16

UP = x - g = 4

ADD

2x = 20

x = 10

ANSWER 10' per second.

(all credit goes to ranjankar at yahoo answer)