Two trains of length 400 m and 200 m are 200 m apart. They start moving towards each other on parallel tracks, at speeds 54 kmph and 36 kmph. After how much time will the trains meet?
Choose the most appropriate option:
A) 8 sec	B) 20 / 7 sec	C) 33 / 7 sec	D) 21 / 7 sec	E) 32 / 7 sec

Rationale: "they are moving in opposite directions , relative speed is equal to the sum of their speeds . relative speed = ( 54 + 36 ) * 5 / 18 = 25 mps . the time required = d / s = 200 / 25 = 8 sec . answer : a"
Answer: A