A train 200m long is moving …

This is because 200/20 = 10 m/s

The answer is 10 seconds

I think some mistake in your question. Length of bridge is also given in question. Not sure but check it

 1 1233288 29.09.2019 India Languages Secondary School +5 pts Answered A train 200 m long moving with a speed of 72 km/hr . Time required by train to cross a bridge which is 1 km long is : 2 SEE ANSWERS Log in to add comment Answer 5.0/5 3  lunchspider Ambitious 20 answers 482 people helped Answer: 60 s or 1 min Explanation: Speed of train is= 20m/s So... In order to cross the bridge 1km long, Train would have to cover the bridge lenght and the train's length itself. So... Total distance the train would have to travel= 1000m+200m=1200m And.. therefore, Time taken by the train to travel 1200m=1200/20 s= 60s Hence the train would take 60s or 1 min to cross the bridge.