TITLE: Simplest error detecting/correcting codes for math newbies
QUESTION [7 upvotes]: Suppose you have been given the task of teaching some basic coding theory to folks who are interested in math but have not taken algebra, number theory, etc. If you want to introduce codes, you might start out with codes that are just based on overall parity - for example, you might start out assuming serial communication, and introduce a code in which $11$ and $00$ were codewords while $01$ and $10$ were not. You can obviously extend this example to any number of bits, but the idea remains the same - and this is a pretty terrible code.
In the spirit of introducing as little abstraction, group theory, etc as possible, what is or are the next logical code(s) to introduce?

REPLY [2 votes]: Maybe the ISBN-Code, demonstrating that it can detect any single altered digit and any transposition of two adjacent digits.
Note that only the older ISBN-10 has this property, but not the newer ISBN-13.