A train B whose length is three times of another A, is running with 58km/hr crosses train A in 15 seconds. Find the length of train A if speed of train A is 50km/hr, if both trains are running in opposite direction?

Let length of train A = L meters. Then length of train B = 3L meters. Speed of A = 50 km/hr, Speed of B = 58 km/hr. Since they run in opposite directions, relative speed = 50 + 58 = 108 km/hr = 108 × (5/18) = 30 m/s. Time to cross = 15 seconds. Total distance covered = L + 3L = 4L. Distance = Speed × Time, so 4L = 30 × 15 = 450, giving L = 112.5 meters.