A train crosses a platform in 30 seconds travelling with a speed of 60 km/h. If the length of the train be 400 metres, then the length (in metres) of the platform is एक रेलगाड़ी एक 60 किमी./घंटा की गति से एक प्लेटफार्म को 30 सेकण्ड्स में पार करती है | यदि रेलगाड़ी की लम्बाई 400 मीटर है, तो प्लेटफार्म की लम्बाई (मीटर में) है |

Speed = 60 km/h = 60 × 1000/3600 = 50/3 m/s. Time taken to cross platform = 30 seconds. Total distance covered = length of train + length of platform = Speed × Time = (50/3) × 30 = 500 meters. Given train length = 400m, so platform length = 500 - 400 = 100 meters. The key is understanding that 'crossing the platform' means covering the train's own length plus the platform's length, and converting units consistently (km/h to m/s).