A train crosses a bridge of length 200 m in 10 seconds and a lamp post on the bridge in 5 seconds. What is the length of the train in metres?  Choose the correct choice
A) 375 m B) 750 m C) 200 m D) 800 m E) 300 m

Rationale: "let length of train = l case - 1 : distance = 200 + l ( while crossing the bridge ) time = 10 seconds i . e . speed = distance / time = ( 200 + l ) / 10 case - 2 : distance = l ( while passing the lamp post ) time = 5 seconds i . e . speed = distance / time = ( l ) / 5 but since speed has to be same in both cases so ( 200 + l ) / 10 = ( l ) / 5 i . e . 2 l = l + 200 i . e . l = 200 answer : option c"
Answer: C