Something you've always wanted to know: why are the introductory courses in college subjects numbered "101"?

Of course, there are exceptions. At NC State the introductory economics course is "201". And at Duke, cutting-edge trailblazers that they are, the introductory economics course is "51D". Followed, naturally, by courses 55D, 105D, and 110D. Superior course numbering--that's why the Dukies are better than everybody else.