Problem 50.

A car goes down a certain road at an average speed of 40 km/h and returns along the same road at an average speed of 60 km/h.  Calculate the average speed for the round trip

Solution:

By definition the average speed is the traveled distance divided by the traveled time. Let introduce L as the traveled distance of the car in one direction. Then the total traveled distance is 2L. Let us find the traveled time. It is

Then the average speed is