A driver covers a certain distance by car driving at 40 km/hr and returns back to the starting point riding on a scooter at 10 km/hr. What was the average speed for the whole journey? Choose the correct choice from the following answers.
A) 12 km/h  B) 14 km/h  C) 16 km/h  D) 18 km/h  E) 20 km/h
time 1 = d / 40   time 2 = d / 10   total time = d/40 + d/10 = d/8   average speed = total distance / total time = 2d / (d/8) = 16 km/h   The answer is 16 km/h.
<result>C</result>
A driver covers a certain distance by car driving at 40 km/hr and returns back to the starting point riding on a scooter at 10 km/hr. What was the average speed for the whole journey?