Two trains of equal length, running with the speeds of 50 and 40 kmph, take 50 seconds to cross each other while they are running in the same direction. What time will they take to cross each other if they are running in opposite directions?  Pick one
A) 5.55 sec  B) 4.55 sec  C) 5.95 sec  D) 6.55 sec  E) 9.55 sec

Rationale: "rs = 50 - 40 = 10 * 5 / 18 = 50 / 18 t = 50 d = 50 * 50 / 18 = 1250 / 9 rs = 50 + 40 = 90 * 5 / 18 = 25 t = 1250 / 9 * 1 / 25 = 5.55 sec answer : a"
Answer: A