Question

A boy while driving to school, his average speed was 20km/hr, and on return journey, the speed was 30km/hr. What was his average speed?

Answer 1

let distance be d km
time for forward journey = distance/speed
=d/20hr
time for backward journey
=d/30hr
average speed =total distance/total time
2d/(d/20+d/30)
= 2d/(5d/60)
=24km/hr