# 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.