gistfile1.rb

class Symbol
  def to_proc
    Proc.new { |*args| args.shift.send(self, *args) }
  end
end

class Fixnum
  def is_a_multiple_of?(multiples)
    multiples.detect { |multiple| (self % multiple).zero? }
  end
end

class Array
  def sum
    self.inject(&:+)
  end
end

module Enumerable
  def multiples_of(*multiples)
    self.select { |i| i.is_a_multiple_of?(multiples) }
  end
end

puts (1..999).multiples_of(3,5).sum