two goods trains each 850 m long are running in opposite directions on parallel tracks . their speeds are 45 km / hr and 30 km / hr respectively . find the time taken by the slower train to pass the driver of the faster one ?
"relative speed = 45 + 30 = 75 km / hr . 75 * 5 / 18 = 125 / 6 m / sec . distance covered = 850 + 850 = 1700 m . required time = 1700 * 6 / 125 = 81.6 sec . answer : b"
add(45, 30)