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?
Answer & explanation
Correct answer: option 3
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