Question

Robin while driving to school computes the
anerage speed for his trip to be 20kniſh on his
return trip along the same route, there is less
traffic and anerage speed is 40 km/h. What is
the average speed for robin trip?​

Answer 1

Let total distance from school to home be s, then

Speed 1 = 20 km/h

Time 1 = s/20 seconds

Speed 2 = 40 km/h

Time 2 = s/40 seconds

Now, Avg. speed = total distance / total time

                             = s / s/20 + s/40

                             = s / 2s + s / 40

                             = s / 3s /40

                             = 40 / 3 km / h