[Note: I'm starting to think that putting difficulty ratings at the beginning of each puzzle was a mistake--so I'm not going to do it this time!]
U.S.A. and Canada were having an argument. I know! How could possibly be unhappy with the U.S.? But that's what happened in this hypothetical. Tempers flared, and before we knew it, each country took action on the other. Previously, the U.S. and Canadian currency had been on equal terms: one dollar to a dollar. But then the U.S. made it law that every Canadian dollar is now only worth ninety cents in U.S. currency. Canada made it law that every U.S. dollar is now only worth ninety cents in Canadian currency.
Charlie, ever the opportunist, found a way to profit from this. He lives near the border, where there are two bars, one on either side. In the bar in the U.S., he uses a U.S. 10 dollar bill to buy a 1 dollar drink, and receives 10 Canadian dollars of change. He walks across the border to the other bar, and buys a 1 dollar drink with his 10 Canadian dollars. He receives 10 U.S. dollars change. He crosses the border again back to the U.S. bar to buy another drink. This process is repeated until he is drunk silly.
Charlie is obviously profiting from this situation. But who is losing?
This is an open-ended problem, so I will not have a separate solution post like I usually do.