Baxter has received a grant to run an environmentally sensitive parking lot downtown. To encourage carpooling, he charges $20 per day per vehicle with only the driver in it and $10 per day for each carpool vehicle with two or more people. On one Monday, 115 vehicles were parked in his lot, and he took in $1990. How many of each kind of vehicle used the lot that day?
Solution
Let represent the number of driver-only cars and the number of carpool cars.
Check:
Suppose a clever little fellow stands outside the parking lot. When he sees a driver-only car approaching, he offers to get in the car as it enters the lot. Thus the driver will save $10, and he is to give half of that to the clever little fellow. Is this a viable scheme? Can the C.L.F. do it again? and again?