Sample output

STAY, 4989 relevant rounds (= 49.9%)
2531 successes (= 50.7%)

CHANGE, 4989 relevant rounds (= 49.9%)
2493 successes (= 50.0%)

wwm-ziegen.rb

num_rounds = 10000
answers    = %W(A B C D)
strategies = %W(STAY CHANGE)

# Helfermethode und Alias für bessere Lesbarkeit
class Array
  def except(element)
    self - [element]
  end
  alias choose_randomly sample
end

strategies.each do |strategy|
  num_successes      = 0
  num_skipped_rounds = 0

  num_rounds.times do
    correct_answer = answers.choose_randomly
    initial_choice = answers.choose_randomly
    joker_result   = [correct_answer, answers.except(correct_answer).choose_randomly].sort
  
    if joker_result.include?(initial_choice)
      final_choice = if strategy == "CHANGE"
        joker_result.except(initial_choice).first
      else
        initial_choice
      end
      success = final_choice == correct_answer
      num_successes += 1 if success
      # puts "#{correct_answer} : #{initial_choice} - #{joker_result.join(' ')} - #{final_choice} : #{success}"
    else
      # puts "#{correct_answer}  : #{initial_choice} - #{joker_result.join(' ')} - SKIPPED"
      num_skipped_rounds += 1
    end
  end

  num_relevant_rounds = num_rounds - num_skipped_rounds
  puts "#{strategy}, #{num_relevant_rounds} relevant rounds (= %.1f%%)" % (num_relevant_rounds * 100.0 / num_rounds)
  puts "#{num_successes} successes (= %.1f%%)" % (num_successes * 100.0 / num_relevant_rounds)
  puts
end