Two trains of equal lengths take 10 sec and 14 sec respectively to cross a telegraph post. If the length of each train be 120 m, in what time will they cross other travelling in opposite direction?  Choose the correct choice from the following:
A) 10	B) 12	C) 13	D) 11.7	E) 15

Rationale: "speed of the first train = 120 / 10 = 12 m / sec . speed of the second train = 120 / 14 = 8.6 m / sec . relative speed = 12 + 8.6 = 20.6 m / sec . required time = ( 120 + 120 ) / 20.6 = 11.7 sec . answer : option d"
Answer: D