If the ratio of the speeds of A and B is a : b, then the ratio of the times taken
by them to cover the same distance is ^{1}/_{a} : ^{1}/_{b}
or b : a.

Suppose a man covers a certain distance at x km / hr and an equal distance at
y km / hr. Then, the average speed during the whole journey is : _{= }^{ 2xy }_{ km/ hr.} ^{x + y}