class Numeric
  @@currencies = {'yen' => 0.013, 'euro' => 1.292, 'rupee' => 0.019, 'dollar' => 1}
  def method_missing(method, *arg)
    singular_currency = method.to_s.gsub(/s$/,'')
    if @@currencies.has_key?(singular_currency)
      self * @@currencies[singular_currency]
    else
      super
    end
  end
  def in(arg)
    singular_currency = arg.to_s.gsub(/s$/,'')
    if @@currencies.has_key?(singular_currency)
      self * @@currencies[singular_currency]
    end
  end
end

puts "5.euro = "+5.euro.to_s
puts "5.euros = "+5.euros.to_s
puts "5.dollars.in(:euros) = "+5.dollars.in(:euros).to_s
puts "10.euros.in(:rupees) = "+10.euros.in(:rupees).to_s