A man takes half time in rowing a certain distance downstream than upstream. What is the ratio of the speed in still water to the speed of current?
- (a) 1 : 2
- (b) 2 : 1
- (c) 1 : 3
- (d) 3 : 1 ✓ UPSC's answer
Why the answer is (d)
• Let the speed in still water be b and the current c. Downstream speed = b + c and upstream speed = b − c.
• For the same distance, half the time means double the speed: b + c = 2(b − c).
• So b = 3c, and b : c = 3 : 1.
• Hence option (d).
Why the other options are wrong
- (a) 1 : 2
- This ratio implies the current is faster than the boat, which would make upstream rowing impossible or require a different time relationship.
- (b) 2 : 1
- This ratio would result in the downstream time being one-third of the upstream time, not half.
- (c) 1 : 3
- This ratio is mathematically impossible for a boat to move upstream, as the current speed would exceed the boat's speed in still water.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2020, held on 4 October 2020. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.