I promise this was the last wordy calculator (Solution)

wordy_calc3.rb

class WordProblem
  def initialize question
    @question = question
  end

  def answer
    if matches.nil?
      raise ArgumentError.new( "Sorry, please enter a valid question." )
    end
    @answer = matches[1].to_i.send( operation(2), matches[3].to_i )
    unless chain.nil?
      @answer = @answer.send( operation(5), matches[6].to_i)
    end
    @answer
  end

  private
  def matches
    @matches = @question.match( pattern )
  end

  def pattern
    /What is (-?\d+) (plus|minus|multiplied by|divided by) (-?\d+)( (plus|minus|multiplied by|divided by) (-?\d+))?\?/
  end

  def operation num
    case matches[ num ]
      when "plus" then :+
      when "minus" then :-
      when "multiplied by" then :*
      when "divided by" then :/
    end
  end

  def chain
    matches[4]
  end
end