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 of the tunnel is?  Choose the correct choice:
A) 200m	B) 776 m	C) 400 m	D) 187 m	E) 1678 m
Speed = 78 * 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.   Answer:400 m
<result>C</result>
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 of the tunnel is?