The portion of the gross profits or income of the investment company to be allocated to the state where the investment company is engaged in business or operating partly within and partly without the state shall be the proportion of the gross profits or income of the investment company determined by dividing the gross amount received, during the year for which the tax is payable, from members, certificate holders or contract holders of the investment company who reside within the state, by the gross amount received during the year from all the members, certificate holders or contract holders, as the case may be, of the investment company, whether the members, certificate holders or contract holders reside within or without this state.