Question

A train crosses a platform in 25 sec. If the train, running at 72 km/hr, is 150m long. find the length of the platform.

Answer 1

72×5/18=20m/s
s=d/t
20=(150+x)/25
150+x=20×25
x=500-150
x=350m

Answer 2

We can solve using this equation:
(length of platform+ length of train) = speed of train * time to cross platform 
So:
x + 150 = 72km/h * 13s
Convert 72km/h to m/s => 72000m/3600s => 20m/s (speed of train)

Now, solve:
x + 150m = 20m/s *13s => x + 150m = 260m => x = 260m - 150m => x = 110m (length of platform)