So,, all that said. If I drove 10 miles at 30 mph and 10 miles at 90 mph my average speed for the 20 miles would be 60 mph.
Uh, NO. 10 miles at 30 mph gonna take 20 minutes. 10 miles at 90 mph gonna take 6 min 40 sec. 20 miles driven in 26 minutes 40 seconds = 45 mph