Code Kata 2: Karate Chop

This kata challenges you to implement binary search in 5 different ways and to document things you had trouble with, like "off by one errors" and fencepost errors.
http://codekata.pragprog.com/2007/01/kata_two_karate.html

Here are my attempts in Ruby.
https://gist.github.com/wmwong/6662429

Got any other ideas on how else to solve this? Or feedback for my code? Let me know down below in the comments!