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.
