Asportsman 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?

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)

step-by-step explanation:

the answer is 128