A person earns Rs. 2000 per month over and above his salary as additional charge allowance. However, 30% of this additional income will be deducted as additional income-tax at source. If the person would deposit Rs. 1000 per month on a long-term saving fetching 12% interest his tax liability on the additional allowance would reduce to 10%. What is the effective interest for this person for money invested in the long-term savings scheme ?