A man runs to a telephone and back in 15 minutes. His speed on the way to telephone is 15 m/s and his speed on the way back is 4m/s. Find the distance to the telephone.

Answer 1

let the time one way be t seconds, then the time the other way has to be 900-t seconds. (15 x 60 seconds = 900 seconds)

distance one way = 15t
distance the other way = 4(900-t)

same distance either way, so
15t = 4(900-t)
19t = 3600
t = 3600/19

distance = 15(3600/19) m or 2842.1 m or appr 2.84 km