A boat can travel 5 km upstream in 15 minutes. If the ratio of the speed of the boat in still water to the speed of the stream is 6 : 1, then how much time will the boat take to cover 19.6 km downstream ?
Answer & explanation
Correct answer: option 3
Upstream Speed = Speed of Boat – Speed of current
Downstream Speed = Speed of Boat + Speed of current
Given,
A boat can travel 5 km upstream in 15 minutes.
The ratio of the speed of the boat in still water to the speed of the stream is 6 : 1
Let the speed of the boat = 6x and the speed of the stream = x
Then, according to the question,
Upstream speed = 6x - x = 5x
= 5x = (5 × 60)÷15
= 5x = 20
= x = 4 km/hr
Downstream speed = 24 + 4 = 28 km/h
Downstream distance = 19.6 km
Time = \(\frac{19.6}{28}\) = 0.7 h. = 42 min.