Mike bought some books that he hoped to earn a $60 \%$ profit after selling them. On the first day, he sold $70 \%$ of his books at a profit of $60 \%$. On the second day, he sold all the remaining books at a discount. If the total profit was $80 \%$ of the planned profit, what would be the discount rate on the second day? 
Overseas Competition->Knowledge Point->Word Problem Modules->Word Problems in Economics->Basic Profit and Loss Concepts