Amendment to section 35C revises deduction computation and clarifies wording of the Explanation for deduction entitlement. The amendment omits the phrase 'a sum equal to one and one-fifth times' from the operative clause, changing the method of computing the deductible amount, and substitutes in the Explanation the phrase 'expenditure with reference to which deduction under this section is to be allowed' with 'expenditure which is to be allowed as deduction under this section', thereby clarifying the description of eligible expenditure.