arithmetic - two trains having equal lengths take 10 seconds and 15 seconds respectively to cross a post if the length of each train is 120 meters in what time in seconds will they cross each other when traveling in opposite direction - skillgun

speed of train1 = 120/10 = 12 m/s
speed of train2 = 120/15 = 8 m/s
if they travel in opposite direction, relative speed = 12+8 = 20 m/s
distance covered = 120+120 = 240 m
time = distance/speed = 240/20 = 12 s