A boat covers a distance of 375 metres upstream in 30 min, and returns back to the starting point in 18 min. Find the ratio of the speed of the boat in still water and the speed of the stream.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 4 : 1.
A boat covers a distance of 375 meters upstream in 30 min, and returns back to the starting point in 18 min.
Let's assume the speed of the boat is x and the speed of stream is y;
Speed = Distance/Time
Upstream speed:
x - y = 375/30...........(1)
Downstream speed:
x + y = 375/18.........(2)
Equation (1) is divided by (2):
(x - y)/(x + y) = (375/30)/(375/18)
⇒ (x - y)/(x + y) = 3/5
⇒ 5x - 5y = 3x + 3y
⇒ 2x = 8y
⇒ x/y = 4/1
Hence,
Ratio of speed of the boat in still water and speed of the stream = x : y = 4 : 1