A 180 meter long train cross another train 120 meter long coming from opposite direction at 30 km/hr in 15 seconds. Find the speed of first train. एक 180 मीटर लम्बी ट्रेन विपरीत दिशा से 30 किमी/घंटे की चाल से आती हुयी, 120 मीटर लम्बी ट्रेन को 15 सेकेण्ड में पार करती है पहली ट्रेन की चाल ज्ञात कीजिये।

Total distance = 180 + 120 = 300 m. Time = 15 seconds. Relative speed = 300/15 = 20 m/s = 20 × (18/5) = 72 km/hr. Let v1 be first train's speed. Since trains move in opposite directions: v1 + 30 = 72, so v1 = 42 km/hr. Standard train problem: add speeds for opposite direction, convert m/s to km/hr by multiplying by 18/5.