The car travels at 100 km/hr for 2.0 hr, at 60 km/h for the next 2.0 h, and finally at 80 km/h for 1.0 h. The average speed of the car over the entire 5 hours has to be determined. This is equal to the total distance traveled in 5 hours divided by 5.
The distance traveled by the car in the first 2 hours is 200 km, it travels 120 km in the next 2 hours and 80 km in the last hour. Adding the distances traveled gives a total of 200 + 120 + 80 = 400 km.
The average speed of the car over the entire 5 hour period is 400/5 = 80 km/h.