def percent_total(amount)
    if self.school.is_mbs
      if mbs_total_sales == 0
        0
      else
        (amount/mbs_total_sales.to_f) * 100
      end
    else
      if total_sales == 0
        0
      else
        (amount/total_sales.to_f) * 100
      end
    end
  end