Set the track length to be a random number, e.g. 5 miles.
Therefore the first two laps took 10 miles ÷ 100 mph = 10 ÷ 100 hours. Similarly, the second two laps took 10 ÷ 102 hours, etc. The total time taken for 40 miles is therefore, 10/100 + 10/102 + 10/140 + 10/150 hours.
Therefore the average speed for the entire 8 laps is 40 ÷ (10÷100 + 10÷102 + 10÷140 + 10÷150) = 119 mph.
My BrainBashers electronic world atlas has developed a fault, I did a listing of miles from England to particular countries and here is the result:
Spain 14,000 miles
Fiji 12,000 miles
Germany 18,000 miles
Brazil 16,000 miles
India 16,000 miles
There are a few more less common words such as menstruum, menstruums, triduum, triduums, weltanschauung, weltanschauungen.