Two trains 180 m and 160 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time which they take to cross each other is?  Choose the correct choice from the following answers: A) 10.7 B) 10.9 C) 10.24 D) 12.24 E) 18.8

Rationale: "relative speed = 60 + 40 = 100 km / hr . = 100 * 5 / 18 = 250 / 9 m / sec . distance covered in crossing each other = 180 + 160 = 340 m . required time = 340 * 9 / 250 = 12.24 sec . answer : d"
Answer: D