1 answer
(click or scroll down)
The average speed on the first route can be calculated as 400 miles divided by 8 hours, which equals 50 mph.
The average speed on the second route can be calculated as 420 miles divided by 7 hours, which equals 60 mph.
Therefore, the average speed on the faster route is 60 mph, while the average speed on the slower route is 50 mph. The difference between the two average speeds is 60 mph - 50 mph = 10 mph.