two trains of length 100 m and 200 m are 100 m apart . they start moving towards each other on parallel tracks , at speeds 72 kmph and 90 kmph . in how much time will the trains cross each other ?
"relative speed = ( 72 + 90 ) * 5 / 18 = 9 * 5 = 45 mps . the time required = d / s = ( 100 + 100 + 200 ) / 45 = 400 / 45 = 80 / 9 sec . answer : b"
divide(100, multiply(add(72, 90), const_0_2778))