Why are introductory classes called "101"?

Why are introductory classes called "101"?

www.slate.com/articles/news_and_politics/.../101_101.html

Traduzir esta página

6 de set de 2006 - The Oxford English Dictionary finds the first use of "101" as an ... In the 1920s, students began to think of college as a means of getting a job, ...