Two trains of length 120 meter and 150 meter crosses a stationary man in 10 and 15 seconds respectively. In what time they will cross each other when they are moving in same direction. Pick
A) 120 sec  B) 125 sec  C) 135 sec  D) 140 sec  E) none of these

Rationale: explanation : 120 = a * 10 , a = 12 m / sec ( speed of first train ) 150 = b * 15 , b = 10 m / sec ( speed of second train ) 270 = ( 2 ) * t , t = 135 seconds answer – c
Answer: C