transaction.rb

  def self.total_volume(transactions)
    total = 0
    if transactions.is_a?(Array)
      transactions.each do |transaction|
        total += transaction.amount
      end
    else
      total += transactions.amount
    end
    total
  end

  def self.total_volume(transactions)
    return transactions.amount unless transactions.is_a? Array
    transactions.reduce(0) do |total, transaction|
      total += transaction.amount
    end
  end