* Guillermo Phillips > Hello All, > > Here's something I've always wondered (perhaps in my naivety). Why > should -1 x -1 = 1? > I appreciate that lots of nice things come from this, but what's the > fundamental reason for it?
Suppose you're a student with no money. However, your old folks are willing to lend you 500$ a month for living. When you borrow 500$ and use them, you actually have -500$. Suppose this have been going on for a while, say ten months, so today your asset is -5000$. How "rich" are you three months from now? That is: -5000$ + -500$ * 3 = -6500$. OK, how "rich" were you 4 months ago? That is: -5000$ + -500$ * -4 = -5000$ + 2000$ = 3000$.