Question

A motor cyclists drive from Ato B eith a uniform speed of 30km /hr and return from place B to A with a uniform speed of 20 km /hr. Find his average speed

Answer 1

Look, question asks for average speed and that is given by
$s = d / t$
where s = average speed, d = total distance and t = total time taken.
In the question, let s be x kms, so from A to B distance = x / 2 and from B to A distance = x / 2
Now, total time would be time taken in one full trip from A  to B and back to A
$t = [\frac{x/2}{30} + \frac{x/2}{20} ]$ hours.
now we have time and total distance.
Simply put them in formula.
average speed = d / t
$t = \frac{x}{ \frac{x/2}{30} + \frac{x/2}{20} }$

I know you can solve it, now. (Y)