Question

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

Answer 1

$average \: speed = \frac{total \: distance}{total \: time }$
$v = \frac{s + s}{ \frac{s}{v1} \frac{s}{v2} }$
$v = \frac{2v1v2}{v1 + v2}$

v=2×20×30/20+30
=1200/50=24km/hr