two trains of length 100 m and 200 m are 70 m apart . they start moving towards each other on parallel tracks , at speeds 54 kmph and 72 kmph . after how much time will the trains meet ?
"they are moving in opposite directions , relative speed is equal to the sum of their speeds . relative speed = ( 54 + 72 ) * 5 / 18 = 7 * 5 = 35 mps . the time required = d / s = 70 / 35 = 2 sec . answer : a"
divide(70, multiply(add(54, 72), const_0_2778))