A one km long train was fast approaching Tunnel no.1, at a distance of 2 + 3/4 km (two and three quarters )km; Tunnel no.1 is 1.5 km long. Further at a distance of 1.75 km Tunnel no. 2 is located , which is of length 1 + 1/2 km.(one and a half )km. Further at a distance of 2.5 km Tunnel no. 3 is located and it is of length 1 km. Find the time elapsed when the train had completely passed through Tunnel no. 3 , If the train took 2.5 minutes to pass through 1 km , uniformly .