स्टेशन A और स्टेशन B के बीच, प्रत्येक स्टेशन से 6 बजे सुबह चलने वाली, दैनिक रेलगाड़ी आरम्भ की जानी है, और यह यात्रा 42 घंटों में पूरी की जानी है। कितनी संख्या में रेलगाड़ियाँ चलानी होंगी जिससे कि शटल सेवा जारी रहे ?
Read this question in English
A daily train is to be introduced between station A and station B starting from each end at 6 AM and the journey is to be completed in 42 hours. What is the number of trains needed in order to maintain the shuttle service?
(a) 2 · (b) 3 · (c) 4 · (d) 7
उत्तर और व्याख्या · explanation in English
Answer: (c) 4
A train leaving at 6 AM arrives 42 hours later, at midnight, and can start back only at the next 6 AM — so each one-way trip uses 2 days and a round trip 4 days. With a departure needed every day, 4 trains keep the shuttle going.
- Leaving A at 6 AM on day 1, a train reaches B 42 hours later — midnight at the end of day 2.
- It starts back from B at 6 AM on day 3 and reaches A at midnight at the end of day 4.
- It leaves A again at 6 AM on day 5: one full cycle takes 4 days.
- A train must leave A every day, so 4 trains are needed (trains 1–4 leave A on days 1–4; train 1 is back for day 5).
- Check: the same 4 trains also give a daily 6 AM departure from B, each leaving B two days after leaving A.
Remember · For a shuttle, find one train's full cycle, waiting included; trains needed = cycle in days × daily departures from one end.
Question and answer: UPSC's official GS Paper II (2016, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·