Durga Ltd. issued 80,000, 10% Debentures of ₹ 100 each at a certain rate of discount and were to be redeemed at a 20% premium. Existing balance of Securities Premium before issuing of these debentures was ₹ 25,00,000 and after writing off Loss on the Issue of Debentures, the balance in Securities Premium was ₹ 5,00,000. At what rate of discount, these debentures were issued?