Say each of four towns is located at the corner of a square. A motorist starts from town A to make a round trip at the following speeds: AB = 30 mph, BC = 40 mph, CD = 50 mph and DA = 60 mph. What is the average speed of the round trip?
Try figuring it out yourselves, readers. The answer appears in the following paragraph.
No, the average speed is not 45 mph. Huh? Consider this example: Say the square is 60 miles on each side. The motorist takes 2 hours to drive AB, 1.5 hours for BC, 1.2 hours for CD and 1 hour for DA. The total distance is 240 miles, and the driving time is 5.7 hours. That’s about 42 mph. Send questions to