A train crosses a bridge of length 800 m in 45 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?	Pick:
A) 375 m	B) 750 m	C) 400 m	D) 800 m	E) 300 m
Let Length of Train = L   Case-1: Distance = 800+L (While crossing the bridge)   Time = 45 Seconds   i.e. Speed = Distance / Time = (800+L)/45   Case-2: Distance = L (While passing the lamp post)   Time = 15 Seconds   i.e. Speed = Distance / Time = (L)/15   But Since speed has to be same in both cases so   (800+L)/45 = (L)/15   i.e. 800 + L = 3L   i.e. 2L = 800   i.e. L = 400   Answer: option 400 m
<result>C</result>
A train crosses a bridge of length 800 m in 45 seconds and a lamp post on the bridge in 15 seconds. What is the length of the train in metres?