an engineer and a physicist are at opposite ends of a football field and a nice crisp $100 is at the 50 yard line, a bell rings and they walk to half the distance, it rings again and they continue splitting the difference, eventually they're both standing a foot away from the bill. at this point the physicist says "if we keep up this pattern we'll never reach the bill", the engineer leans over and picks up the bill and says "eh, close enough".

thats one I got from here
http://ask.metafilter.com/mefi/3893