Sunil can row a boat 20 km upstream in 1 hour 15 minutes. If the speed of the current of the river is 2 km/h, then how much time will he take to row the boat 30 km downstream?

1 h 30 m

Upstream Speed = Speed of Boat – Speed of current

Downstream Speed = Speed of Boat + Speed of current

We know that,

1 hr 15 minutes = 1 + \(\frac{1}{4}\) = \(\frac{5}{4}\)= hours

Let the speed of the boat in still water = x km/hr

Upstream Speed = (x – 2) km/hr

According to the question,

(x - 2) × \(\frac{5}{4}\) = 20

= x - 2 = 16

= x = 18

Downstream Speed = 18 + 2 = 20 km/hr

Time is taken by boat to cover 30 km downstream = \(\frac{30}{20}\) = 1.5 hr