Two trains travel in opposite directions at 36 kmph and 45 kmph and a man sitting in slower train passes the faster train in 4 seconds. The length of the faster train is	Pick one:	A) 80 m	B) 100 m	C) 90 m	D) 180 m	E) none

Rationale: solution relative speed = ( 36 + 45 ) km / hr = ( 81 x 5 / 18 ) m / sec = ( 45 / 2 ) m / sec length of the train = ( 45 / 2 x 4 ) m = 90 m . answer c
Answer: C