http://vladimir-vg.github.com/2011/05/16/about-monkey-patching/

gistfile1.rb

1.year + 2.months + 3.weeks    # => 1 year, 2 months, and 21 days 
2.hours + 30.minutes           # => 9000 seconds 

gistfile2.txt

$> rvm use rbx
Using /home/v/.rvm/gems/rbx-head
$> rails c
Loading development environment (Rails 3.0.7)
>> a = 3
 => 3 
>> a.method :weeks
 => #<Method: Fixnum#weeks (defined in Numeric at <skipped>/gems/activesupport-3.0.7
                                                           /lib/active_support
                                                           /core_ext/numeric
                                                           /time.rb:52)> 

gistfile3.rb

def weeks
  ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]])
end
alias :week :weeks

gistfile4.txt

>> Numeric.subclasses 
 => [Float, Integer, BigDecimal, Date::Infinity, Rational]

gistfile5.txt

>> Numeric.instance_methods - Object.instance_methods
 => ["fdiv", "<=>", "zero?", "abs", "ceil", "step", "remainder",
     "coerce", "initialize_copy", "truncate", "to_int", "modulo",
     "+@", "div", "integer?", "nonzero?", "floor", "redo_compare",
     "-@", "divmod", "quo", "round", ">", ">=", "<", "<=", "between?"] 

gistfile6.txt

>> a = ActiveSupport::Duration.new 100, [[:seconds, 100]]
 => 100 seconds 
>> a.class
 => Fixnum