how much time will a train of length 420 m moving at a speed of 72 kmph take to cross another train of length 640 m , moving at 36 kmph in the same direction ?
"the distance to be covered = sum of their lengths = 420 + 640 = 1060 m . relative speed = 72 - 36 = 36 kmph = 36 * 5 / 18 = 10 mps . time required = d / s = 1060 / 10 = 106 sec . answer : e"
divide(add(420, 640), multiply(subtract(72, 36), const_0_2778))