A boat's speed in still water is 45 km/h, while the river is flowing at a speed of 15 km/h. The time taken to cover a certain distance upstream is 9 hr more than the time taken to cover the same distance downstream. Find the distance (in km).
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 540.
Given that:
A boat's speed in still water is 45 km/h
The speed of the river =15 km/h
Hence,
The speed of the boat upstream = 45 - 15 = 30 km/h
The speed of the boat downstream = 45 + 15 = 60 km/h
Let the distance covered by the boat be D
According to the question:
(Time)upstream = (Time)downstream + 9
⇒ D/30 = D/60 + 9
⇒ D/30 - D/60 = 9
⇒ (2D - D)/60 = 9
⇒ D = 9 × 60 = 540
Hence,
Distance = 540 km