Your friend tells you that if you let him keep 50 of your Pokemon cards for a month, he will give you 1 extra card when he returms your cards. What is the annual rate of interest he is willing to pay for the borrowed cards?

The management of a supermarket wants to adopt a new promotional policy of giving a free gift to every customer who spends more than a certain amount per visit at this supermarket. the expectation of the management is that after this promotional policy is advertised, the expenditures for all customers at this supermarket will be normally distributed with a mean of $95 and a standard deviation of $20. if the management wants to give free gifts to at most 10% of the customers, what should the amount be above which a customer would receive a free gift?