(3)In cases falling under sub-section (2)(b), where the income liable to tax cannot be definitely ascertained, or can be ascertained only with an amount of trouble and expense to the assessee, which is unreasonable, the rules made under this section may—(a)prescribe methods by which an estimate of such income may be made; and(b)in cases of income derived in part from agriculture and in part from business, specify the proportion of the income which shall be deemed to be income liable to tax, and an assessment based on such estimate or proportion shall be deemed to be duly made as per this Act.
