CSAT 2020

Q. A man takes half time in rowing a certain distance downstream than upstream. What is the ratio or the speed in still water to the speed of current?

(a) 1:2
(b) 2:1
(c) 1:3
(d) 3:1
Correct Answer: (d) 3:1

Question from UPSC Prelims 2020 CSAT Paper

Explanation :

Rowing & Speed of Current

Let’s say the speed of the man in still water is v and the speed of the current is c. When rowing downstream (with the current), his effective speed would be (v + c). When rowing upstream (against the current), his effective speed would be (v – c).

According to the problem statement, it takes him half as much time to row a certain distance downstream than upstream. Since time = distance/speed, this means that his downstream speed must be twice his upstream speed: (v + c) = 2(v – c).

Solving this equation for v and c, we get: v = 3c.

So the ratio of the man’s speed in still water to the speed of the current is 3:1.

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