Train A running at 81 km/h takes 72 sec to overtake train B, when both the trains are running in the same direction, but it takes 36 sec to cross each other if the trains are running in the opposite direction. If the length of train B is 600 meters, then find the length of train A (in meters)

Given- speed of A = 81km/h, distance of B = 600m Let speed of B = B, and distance of A = x  When both the trains are running in the same direction  (A – B) × 72 = x + 600 5/18 (81 – B) × 72 = x + 600 ... (1) When both the trains are running in the opposite direction  5/18 (81 + B) × 36 = x + 600 ... (2) From (1) and (2) 5/18 × (81 – B)72 = (81 + B) 36 ×5/18  81 × 2 – 2B = 81 + B 3B = 81  B = 27  Put the value of B in (1)  (81 – 27) × 72 × 5/18 = x + 600  1080 – 600 = x  x= 480 m