Abdul while driving to school, computes the average speed for his trip to be `20 kmh^(-1)`. On his return trip along the same route, there is less traffic and the average speed is `40 kmh^(-1)`. What is the average speed for Abdul's trip ?

Explanation

Let `t_(1)` and `t_(2)` be the time taken by Abdul to ge to school and come back from the school respectively. Let s be its distance covered one way, then
`t_(1)=(s)/(20)h` and `t_(2)=(s)/(40)h`
Total time taken `=t_(1)+t_(2)=(s)/(20)+(s)/(40)=(3s)/(40)h`
Total distance covered = 2s
`therefore` Average speed `=(2s)/(3s)xx40=(80)/(3)=26.67 kmh^(-1)`