A train travelling at 48 kmph completely crosses another train having half its length and travelling in opposite direction at 42 kmph, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the platform is

We are given the following:

• Train A speed = 48 km/h
• Train B speed = 42 km/h
• Train B is half the length of Train A
• Time to cross Train B = 12 seconds
• Time to cross a platform = 45 seconds

Step 1: Convert speeds to m/s
Speed of Train A = 48 × 5/18 = 13.33 m/s Speed of Train B = 42 × 5/18 = 11.67 m/s

Step 2: Relative speed while moving in opposite directions
Relative speed = 13.33 + 11.67 = 25 m/s

Step 3: Crossing time = 12 s, total distance = L + L/2 = 3L/2
3L/2 = 25 × 12 = 300 L = 200 meters

Step 4: Train passes a platform in 45 seconds
Speed of train = 13.33 m/s Distance = 13.33 × 45 = 600 meters Platform length = 600 – 200 = 400 meters

Final Answer:
The length of the platform is 400 meters.