Abdul, while driving to school, computes the average speed for his trip to be 20 km.h–1. On his return trip along the same route, there is less traffic and the average speed is 30 km.h–1. What is the average speed for Abdul’s trip?

Solution

Distance travelled to reach the school = distance travelled to reach home = d (say)

Time taken to reach school = t₁

Time taken to reach home = t₂

therefore, average speed while going to school = total distance travelled/ total time taken = d/t₁ = 20 kmph

Average speed while going home = total distance travelled/ total time taken = d/t₂= 30 kmph

Therefore, t₁ = d/20 and t₂ = d/30

Now, the average speed for the entire trip is given by total distance travelled/ total time taken

= (d+d)/(t₁+t₂)kmph = 2d/(d/20+d/30)kmph

= 2/[(3 + 2)/60]

= 120/5 kmh^-1 = 24 kmh^-1

Therefore, Abdul’s average speed for the entire trip is 24 kilometers per hour.