Bill Clinton, Forty-Second President of the United States. Public Domain Image from NARA
1 Total vehicle miles driven by teen drivers have plummeted, not only because a smaller share of them are driving but also because miles per young driver have also declined.  In 1990, each driver aged 16 to 19 drove an average of 8,485 miles per year.
8. Divide total miles by total gallons. Use your trip odometer to see how many miles you traveled total, then divide this by gallons to get your average fuel consumption. While this is the exact number of miles per gallon during your test period, it is a good estimate for your car's average fuel consumption. For example, if you used 25 gallons of gas, and drove 500 miles during that time, then your average fuel consumption would be 20 miles per gallon (500 miles / 25 gallons = 20 mpg).