In a 120-mile trip, the first 40 miles were completed at 60 mph. If the average speed for the whole trip was 50 mph, what was the average speed in the last 80 miles? Choose the correct option:
A) 585/13 mph  B) 590/13 mph  C) 595/13 mph  D) 600/13 mph  E) 605/13 mph
The time to complete the first 40 miles was (40 miles / 60 mph) = (2/3) hours.   The time to complete the whole trip was (120 miles / 50 mph) = (12/5) hours.   The time to complete the last 80 miles was (12/5) - (2/3) = (26/15) hours.   The average speed in the last 80 miles was (80 miles / (26/15) hours) = 600/13 mph.   The answer is 600/13 mph.
<result>D</result>
In a 120-mile trip, the first 40 miles were completed at 60 mph. If the average speed for the whole trip was 50 mph, what was the average speed in the last 80 miles?