A train travelling at 36 kmph crosses a platform in 20 seconds and a man standing on the platform in 10 seconds. What is the length of the platform in meters?

Speed of the Train = 36 km/hr.
= 36 × 5/18 [Changing into m/s]
= 2 × 5
= 10 m/s.

Time taken to cross the Platform = 20 seconds.
Time taken to cross the man = 10 seconds.
∵ Speed of the Train = Length of the Train/Time to cross the Man

∴ Length of the Train = Speed of the Train × Time to cross the Man.
= 10 × 10
= 100 m.
Sum of the Length of Platform and train = Speed of the Train × Time taken by the Train to cross the Platform.
= 10 × 20
= 200 m.
∵ Length of the Train + Length of the Platform = 200
∴ 100 + Length of the Platform = 200
∴ Length of the Platform = 200 - 100
= 100 m.
∴ Length of the Platform is 100 m.