policy_class.rb

class Policy
  def price
    @price = Settings.policy.base_rate + Settings.policy.extra_traveller_discount * (@travellers.length - 1)
    @travellers.each do |traveller|
      @price += @destination.day_rate(traveller.age) * (@end_date - @start_date).to_i
    end
  end
end

class Destination
  def day_rate(age)
    @day_rate * Statistics.function(Setting.policy.optimal_age, age)
  end
end

policy_class_refactored.rb

class Policy
  def price
    @price = base_rate + Settings.policy.multi_traveller_discount * (@travellers.length - 1)
    @travellers.each do |traveller|
      @price += trip_price(traveller)
    end
  end
  
  private
  
  def base_rate
    Settings.policy.base_rate
  end
  
  def multi_traveller_discount
    Settings.policy.multi_traveller_discount
  end
  
  def trip_price(traveller)
    @destination.day_rate(traveller.age) * trip_length
  end
  
  def trip_length
    (@end_date - @start_date).to_i
  end
end

pricing_module.rb

class Policy
  def price
    Policy::Pricing.base_price(Settings.policy.base_rate, Settings.policy.multi_traveller_discount, @travellers.length) +
    @travellers.reduce(:+) { |traveller| Policy::Pricing.traveller_trip_price(Setting.policy.optimal_age, traveller.age, @destination.day_rate, trip_length) }
  end
end

class Destination
  attr_reader :day_rate
end

module Policy::Pricing
  def base_price(base_rate, multi_traveller_discount, number_of_travellers)
    base_rate + (1 - multi_traveller_discount) * (number_of_travellers - 1)
  end
  module_function :base_price
  
  def traveller_trip_price(optimal_age, traveller_age, day_rate, trip_length)
    day_rate * Statistics.function(optimal_age, traveller_age) * trip_length
  end
  module_function :traveller_trip_price
end