When you enter the alaska turnpike, they give you a ticket showing the time and place of your entry.
when you exit, you turn in this ticket and they use it to figure your toll. because they know the
distance between toll stations, they can also use it to check your average speed against the turnpike
limit of 65 mph. on your trip, heavy snow limits your speed to 40 mph for the first 120 miles. at
what average speed can you drive for the remaining 300 miles without having your ticket prove that
you broke the speed limit? (legally, you cannot drive this fast.)