(a) the amount arrived at by applying the following formula- rate of tax x aggregate of sale prices -----------------------: 100 plus rate of tax Provided that no deduction on the basis of the above formula shall be made if the amount by way of tax collected by a registered dealer, in accordance with the provisions of this Act, has been otherwise deducted from the aggregate of sale prices. Explanation.-- Where the turnover of a dealer is taxable at different rates, the aforesaid formula shall be applied separately in respect of each part of the turnover liable to a different rate of tax;