The Laquedemitasse's math homework includes some simultaneous-equation story problems, along the lines of "Three years ago Fred was three times as old as Paul was, and two years from now Fred will be twice as old as Paul. How old are Fred and Paul now?"
It's not a very realistic problem, for in the real world, we would just ask Fred and Paul to tell us their ages. It occurred to me, however, with some inspiration from Professor Bogdanski, that our metropolitan area offers us raw material for these problems. Consider this one.
A transit district operates X miles of bus service and Y miles of light rail. For every additional mile of light rail that it constructs and operates, it must cut Z miles of bus service to pay for the additional light rail. How many more miles of light rail can it build and operate before it will have no bus service at all?