一、何謂「Plimsoll Mark」(或稱為「Load Line Marks」),試繪圖並詳細說明之。

4. (12分) Commercial kerosene is stocked in a bulk tank at the beginning of each week.Because of limited supplies, the proportion X of the capacity of the tank available for sale and the proportion Y of the capacity of the tank actually sold during the week are continuous random variables. Their joint distribution is given byFind the covariance of X and Y.