On a trip a motorist travels at 80 km/h for the first 200 km, and 60 km/h for the remainder of the trip. If the trip is 300 km in total, calculate the average speed for the whole trip.
The average speed is equal to the total distance over total time. We can first find the time taken for each parts of the trip, since we already have the total distance.
Time taken for first part: 200/80 = 2.5h
Second part: 100/60 = 5/3h
Now find the average speed: 300/(2.5+5/3) = 72km/h
