@stevenstrogatz reposts a clever, simple problem:
two people climb a staircase and then climb an escalator. One person rests a minute on the staircase and the other rests a minute on the escalator, but otherwise they climb stairs at the same rate. Who is faster or are they equally fast?
There’s also an airport-walkway version that adds special relativity as a twist.
It’s interesting to see the varied thought processes in the comments. Pencil and paper is often quicker and yields useful analytic insight, but these are both accumulation problems, and therefore good candidates for SD simulation.
How would you model this situation? (I’ll post my answer in a day or two.)