A car travels at a speed of 30 mph over a certain distance, and then returns over the same distance at a speed of 20 mph. What is the average speed for the total trip?
Answer
24 mph. Most people are quick to answer 25 mph, but this is not correct, as we will see. Let the distance travelled be 60 miles each way. Then, the trip out = 60/30 = 2 hours, and the trip back = 60/20 = 3 hours. Therefore the 120-mile trip = 120/5 = 24 mph.
