The speed of a boat in still water is thrice the speed of the stream. If the boat takes 15.5 seconds to go to a certain place downstream, then find the additional time required to cover the same distance travelling upstream.
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 15.5 sec
Given that the speed of boat in still water is thrice the speed of stream.
Let, the speed of the boat in still water and the speed of a stream be 3x and x respectively;
So,
Downstream speed = 3x + x = 4x
Upstream speed = 3x - x = 2x
Given that;
The boat takes 15.5 sec to go to a certain place downstream.
Let the time taken to cover the same distance travelling upstream be T;
So,
Distance:
Downstream speed × time = Upstream speed × T
⇒ 4x × 15.5 = Upstream speed × T
⇒ 4x × 15.5 = 2x × T
⇒ T = 15.5 × 2 = 31
Hence,
Additional time required to cover the same distance = 31 - 15.5 = 15.5 sec