1.Cooper plans to sell four units (A,B,C,D) of eReaders in the coming season. He can buy the product from the producer, with two options: (i) buy one month before the season, when demand is still uncertain (normally distributed N(,²), see Table 1); (ii) buy one week before the season, when demand is certain. Cooper decides to buy some types through option (i), and buy the rest types through option (ii).

(a)If Cooper uses option (i) to buy A, what is the chance that he has over 1000 units of A left at the end of the season?

(b)To use option (ii), Cooper must buy at least 1800 units through option (i). How many units should he buy through option (i)?