An automobile travels from city A to city B and returns to city A by the same route

Q. An automobile travels from city A to city B and returns to city A by the same route. The speed of the vehicle during the onward and return journeys were constant at 60 km/h and 90 km/h, respectively. What is the average speed in km/h for the entire journey?

            (A) 72               (B) 73                         (C) 74                         (D) 75

Ans: 72

Sol:

Total distance=x

(Onward journey) S1=60km/h
(Return journey) S2=90km/h