Mathematics · Discount

The marked price of an article is Rs. 10,000. Under a cash payment plan, a 20% flat discount is offered. Under an installment plan, the customer pays a down payment and subsequent installments which effectively reduces the discount availed compared to the marked price. If the total amount paid in the installment plan amounts to Rs. 9,000, find the percentage of net discount availed by the customer relative to the marked price when he opts for this installment plan.