4,000 notebooks with a cost of 3.5 yuan are sold at a price of 50% of the profit. When 80% of the notebooks are sold, the remaining notebooks are sold at a discount. The profit obtained is 88% of the predetermined profit. How much discount?
成本为3.5元的笔记本4000本，按50%的利润定价出售，当售出80%后，剩下的笔记本打折出售，结果获得的利润是预定的88%，剩下的笔记本出售时按定价打了几折？
<result>8</result>