The ratio of time taken by a boat to cover a distance in downstream to that of in upstream is 3 : 5. If the boat covers 90 km in downstream in t hours and 72 km in upstream in (t+1) hours, then find downstream speed (in km/hr) of the boat.

Correct option is D

Let speed of boat in still water be x km/hr and speed of stream be y km/hr

From (i) and (ii) we get –
y = 6
So, x = 24
Required speed = (24+6) = 30 km/hr