Answer:
26 2/3
Step-by-step explanation:
Average speed is total distance divided by total time.
The time for the first trip was ...
(90 mi)/(20 mi/h) = 4.5 h
The time for the return trip was ...
(90 mi)/(40 mi/h) = 2.25 h
Then the average for the trip and return is ...
total miles/total time = (90 +90)/(4.5 +2.25) = 26 2/3 . . . . mi/h
The average speed for the round trip was 26 2/3 miles per hour.
