$ ruby add_many_numbers.rb
...ruby-2.2.3/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require': cannot load such file -- addition (LoadError)
        from ...rvm/rubies/ruby-2.2.3/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
        from add_many_numbers.rb:4:in `<main>'
$