1. Suppose the original price is X yuan, that is, X-72=72*25% and X=90. So the original daily profit is 100*(90-72)= 1800 yuan, and the profit after price change is (90 * 90%-). If the selling price is Y yuan, it is: (y-x) * (1+8%) = y-x * (1-6.4%), and the profit rate is) (Y-X)/X = (1. If you apply for a membership card, the price is 20+200*80%= 180 yuan, so it is cost-effective to apply for a membership card. (3) to buy 60 yuan's books, if you apply for a membership card, the price is 20+60*80%=68 yuan, so it is cost-effective not to apply for a membership card.