Average speed = (total distance) / (total time)
Distance during the first hour = (80 km/hr) x (1 hr) = 80 km
Distance during the next 2 hours = (40 km/hr) x (2 hrs) = 80 km
Total distance = 80 km + 80 km = 160 km.
Total time = 1 hr + 2 hrs = 3 hrs
Average speed = (160 km) / (3 hrs) = (53 and 1/3) km/hr.
