A moving train crosses a man standing on a plat form  and a bridge 300 meters long in 10 seconds and 25seconds respectively. What will be the time taken by the train to cross a platform 200 meters long?

Given that a moving train crosses a man standing on a plat form  and a bridge 300 meters long in 10 seconds and 25seconds respectively

The train crosses the platform whose lenght is 300 meters in $25-10=15$ sec

Hence, the speed of the train is $\frac{300}{15}=20 m/sec$

The length of the train is $10·20=200 meters$

Time taken by the train to cross the platform 200 meters long is $\frac{200+200}{20}=20 sec$