Two tains of equal lengths take 10 seconds and 20 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction? Select:
A) 12 B) 14 C) 16 D) 20 E) 13.3

Rationale: "sol . speed of the first train = [ 120 / 10 ] m / sec = 12 m / sec . speed of the second train = [ 120 / 20 ] m / sec = 6 m / sec . relative speed = ( 12 + 6 ) = m / sec = 18 m / sec . ∴ required time = ( 120 + 120 ) / 18 secc = 13.3 sec . answer e"
Answer: E