A boat covers 120 km downstream in five hours and difference between downstream and upstream speed is 3 km/hr. Find the ratio of the speed of boat in still water to the speed of stream?

Correct option is D

Downstream speed of the boat = 120/5 = 24 km/hr

We know, always downstream speed > upstream speed

upstream speed of the boat = 24 – 3 = 21 Km/hr

So, still water speed of the boat = (24+21)/2 = 45/2=22.5 km/hr

And speed of stream = (24-21)/2 = 3/2=1.5 km/hr

Required ratio = 22.5 : 1.5 = 15 : 1