Question

In driving the usual route to school Shyam computes the average speed for the trip to be 20 km/h. On the return trip along the same route, there is less traffic and the average speed is 40 km/h, What is
the average speed for Shyam's total trip ?

Answer 1

Suppose the distance to school is d Ian. Then, Time taken to drive to school $=\frac{Distance}{Speed}=\frac{dkm}{20km/h}=\frac{d}{20}h$ Time taken in returning by. the same route $=\frac{dkm}{40km/h}=\frac{d}{40}h$ Total time $=\frac{d}{20}h+\frac{d}{40}h=\frac{2d+d}{40}h=\frac{3d}{40}h$ $\therefore$ Average speed $=\frac{Distance}{Time}=\frac{2dkm}{\frac{3d}{40}h}$ $=\frac{2\times 40}{3}km/h=\frac{80}{3}km/h=26.66km/h=26.7km/h$. (to 1 dp)