The speed of a boat in still water is 18 km/h and the speed of the current is 6 km/h. In how much time (in hours) will the boat travel a distance of 90 km upstream and the same distance downstream?

Solution (By Examveda Team)

$$\eqalign{ & \frac{{90}}{{{\text{Boat}} - {\text{Stream}}}} + \frac{{90}}{{{\text{Boat}} + {\text{Stream}}}} = {\text{Time}} \cr & \frac{{90}}{{12}} + \frac{{90}}{{24}} = {\text{Time}} \cr & {\text{Time}} = \frac{{270}}{{24}} = \frac{{45}}{4} = 11\frac{1}{4} \cr} $$