A train 1200 m long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 min, then the length of the tunnel is?  Choose the correct choice from the following answers:
A) 2898
B) 277
C) 500
D) 100
E) 435
Speed = 78 * 5/18 = 65/3 m/sec.   Time = 1 min = 60 sec.   Let the length of the train be x meters.   Then, (1200 + x)/60 = 65/3   x = 100 m.   Answer: 100
<result>D</result>
A train 1200 m long is running at a speed of 78 km/hr. If it crosses a tunnel in 1 min, then the length of the tunnel is?