A train 900 m long is running at a speed of 78 km hr If it crosses a tunnel in 1 min then the length...........

Explanation:

Speed = 78 x 5/18 = 65/3 m/sec.
Time = 1 min = 60 sec.
Let the length of the train be x meters.
Then, (900 + x)/60 = 65/3
x = 400 m.

Hence, option 1 is the correct answer.