From a photograph one observes that on a level section of highway 10% of the vehicles are trucks, 90% are cars, and that there are 50 vehicles per mile of highway. The trucks travel at 40 mph, and the cars at 50 mph. This highway also has a section with a steep grade on which the speed of the trucks drops to 20 mph, and the speed of the cars to 40 mph. No vehicles enter the observed sections of highways (except at the ends), and the flows are (nearly) stationary.
Determine:
(a) The flow of vehicles on the level section.
(b) The density of vehicles on the grade.
(c) The percent of trucks on the grade as seen on a photograph.
(d) The percent of trucks as seen by a stationary observer on the grade