(5)Notwithstanding anything contained in any other provision of this Act, the profits and gains of an eligible business to which the provisions of sub-section (1) apply shall, for the purposes of determining the quantum of deduction under that sub-section for the assessment year immediately succeeding the initial assessment year or any subsequent assessment year, be computed as if such eligible business were the only source of income of the assessee during the previous year relevant to the initial assessment year and to every subsequent assessment year up to and including the assessment year for which the determination is to be made.