Find avrg speed if a man travels at speed of 18km/hr up and 24km/hr dawn at an altitude of 300m.  Answers
A) 25.8  B) 26.8  C) 27.8  D) 20.5  E) 21.8

Rationale: "avg speed = 2 * x * y / ( x + y ) = 2 * 18 * 24 / ( 18 + 24 ) = 20.5 answer : d"
Answer: D