gistfile1.rb

  def charity_donations_total_amount
    charity_donations.reduce(0) do |sum, charity_donation|
      sum + charity_donation.total_amount
    end
  end

  # versus

  def charity_donations_total_amount
    sum = 0
    charity_donations.each do |charity_donation|
      sum += charity_donation.total_amount
    end
    sum
  end