two trains are moving in opposite directions at 60 km / hr and 90 km / hr . their lengths are 1.9 km and 2.1 km respectively . the time taken by the slower train to cross the faster train in seconds is ?
"relative speed = 60 + 90 = 150 km / hr . = 150 * 5 / 18 = 125 / 3 m / sec . distance covered = 1.9 + 2.1 = 4 km = 4000 m . required time = 4000 * 3 / 125 = 96 sec . answer : d"
subtract(divide(multiply(1.9, const_1000), divide(multiply(60, const_1000), const_3600)), divide(multiply(2.1, const_1000), divide(multiply(90, const_1000), const_3600)))