Abdul while driving to school, computes the average speed for his trip to be `20 kmh^(-1)`. On his returen 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 ?

Answer

26.67 km/h

Explanation

Let the school be at a distance of `x km`. If `t_(1)` time taken to reach the school, then
`t_(1) = ("distance")/("average speed") = (x)/(20)`
If `t_(2)` is time taken to reach back, then
`t_(2) = ("distance")/("average speed") = (x)/(40)`
total time, `t = t_(1) + t_(2) = (x)/(20) + (x)/(40) = x[(1)/(20) + (1)/(40)] = (6x)/(80) = (3x)/(40)`
total distance `= x + x = 2 x`
`"Average speed" = ("total distance")/("total time") = (2x)/(3x//40) = 26.67 km//h`