A train travelling at a speed of 30 m/sec crosses a platform, 600 metres long in 30 seconds. The length (in metres) of train is :

Answer: Option D

Total distance covered by the train in 30 seconds with the speed of 30 m/s is
= 30 × 30 m/s
= 900 metres
Total distance - train's length + platform's length
900 = train's length + 600
(when train crosses platform it covers length equal to length of train + length of platform)
Train's length = 900 - 600
Train's length = 300 metres