a train covers a distance of 20 km in 30 min . if it takes 18 sec to pass a telegraph post , then the length of the train is ?
"speed = ( 20 / 30 * 60 ) km / hr = ( 40 * 5 / 18 ) m / sec = 100 / 9 m / sec . length of the train = 100 / 9 * 18 = 200 m . answer : e"
divide(20, subtract(divide(20, 30), 18))