Odin project of Test First's Learn Ruby
Links for more info
http://www.theodinproject.com/web-development-101/ruby
http://testfirst.org/learn_ruby
Utilized many ruby concepts and methods for solving problems.
Some of these are Strings, Integers, Floats, Arrays, Hashes, functions, classes, methods, iterating, looping, ternary operator, modules, blocks, yield, stubs, class and instance variables, modular arithmetic, regular expressions, open classes, method_missing and passing symbols of functions.
Starts off easy but exercises 12 - 15 give the opportunity to use many interesting concepts.