A car is scheduled to make a 616-mile trip in 9 hours. The car averages 60 mph during the first 240 miles and 80 mph during the next 160 miles. What must the average speed of the car be for the remainder of the trip in order for the car to arrive on schedule?
In the first 240 miles, the car travel at the time:
240 : 60 = 4 (hrs)
In the next 160 miles, the car travel at the time:
160 : 80 = 2 (hrs)
The time remaining is: 9 - 4 - 2 = 3 (hrs)
The distance remaining is: 616 - 240 - 160 = 216 (miles)
The average speed of the car before the remainder of the trip in order for the car to arrive on schedule is: 216 : 3 = 72 (mph)