A 300 m long train crosses a platform in 39 sec while it crosses a signal pole…

Answer: 350 m

Let the platform length be x metres. The train length is 300 m.

1. Step 1: Find the speed of the train using the time to cross a pole.

   Speed = train length / time = 300 / 18 = 50/3 m/s.

2. Step 2: Use the time to cross the platform.

   (300 + x) / (50/3) = 39

   Solve: 300 + x = 39 * (50/3) = 650

   Thus x = 650 - 300 = 350 m.

Therefore, the length of the platform is 350 m.