एक व्यक्ति को धारा की उल्टी दिशा में जाने की अपेक्षा धारा प्रवाह की दिशा में किसी निश्चित दूरी को नाव द्वारा खेने में आधा समय लगता है। अचल पानी में चाल का, धारा की चाल से अनुपात क्या है?
Read this question in English
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
उत्तर और व्याख्या · explanation in English
Answer: (d) 3 : 1
Half the time over the same distance means the downstream speed is twice the upstream speed. So b + c = 2(b − c), which gives b = 3c: still-water speed : current = 3 : 1.
- Let the speed in still water be b and the current c.
- Downstream time is half the upstream time, so downstream speed = 2 × upstream speed.
- b + c = 2(b − c), so b = 3c.
- b : c = 3 : 1.
- Check: b = 3, c = 1 gives speeds 4 and 2 — half the time downstream.
Remember · Same distance: time ratio is the inverse of speed ratio. Downstream = b + c, upstream = b − c.
Question and answer: UPSC's official GS Paper II (2020, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·