एक मालगाड़ी दिल्ली से मुंबई के लिए 40 km प्रति घंटे की औसत चाल से रवाना होती है। उसके दो घंटे पश्चात् एक एक्सप्रेस गाड़ी दिल्ली से मुंबई के लिए, पहले रवाना हुई मालगाड़ी के समांतर पथ पर, 60 km प्रति घंटे की औसत चाल से रवाना होती है। दिल्ली से कितनी दूरी पर एक्सप्रेस गाड़ी, मालगाड़ी से मिलेगी?
Read this question in English
A freight train left Delhi for Mumbai at an average speed of 40 km/hr. Two hours later, an express train left Delhi for Mumbai, following the freight train on a parallel track at an average speed of 60 km/hr. How far from Delhi would the express train meet the freight train?
(a) 480 km · (b) 260 km · (c) 240 km · (d) 120 km
उत्तर और व्याख्या · explanation in English
Answer: (c) 240 km
The freight train has an 80 km lead when the express starts. The express closes the gap at 20 km/h, taking 4 hours, by which time it has run 60 × 4 = 240 km from Delhi.
- Lead of the freight train when the express starts = 40 × 2 = 80 km.
- Relative speed = 60 − 40 = 20 km/h, so time to catch up = 80 ÷ 20 = 4 h.
- Distance of the express from Delhi = 60 × 4 = 240 km.
- Check: the freight train has run 40 × 6 = 240 km in 6 hours.
Remember · Catch-up time = head start ÷ relative speed; then distance = the chaser's speed × that time.
Question and answer: UPSC's official GS Paper II (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). ·