A train running at a speed of 36 kmph crosses an electric pole in 12 seconds. In how much time will it cross a 390 m long platform?
Answers:
A) 19
B) 27
C) 51
D) 47
E) 28

Rationale: "let the length of the train be x m . when a train crosses an electric pole , the distance covered is its own length . so , x = 12 * 36 * 5 / 18 m = 120 m . time taken to cross the platform = ( 120 + 390 ) / 36 * 5 / 18 = 51 min . answer : c"
Answer: C