bookstore/app/presenters/books_presenter.rb

class BooksPresenter < SimpleDelegator
  include ActiveSupport::NumberHelper

  def price
    super / 100
  end

  def price_with_currency
    number_to_currency(price)
  end

  def authors
    super.map { |author| "#{author.first_name} #{author.last_name}" }.join(', ')
  end
end