1 I have 100 items of a product in stock. The probability mass function for the product’s demand D is P(D = 90) =

P(D = 100) = P(D = 110) =1/3 .

a Find the mass function, mean, and variance of the number of items sold.

b Find the mass function, mean, and variance of the amount of demand that will be unfilled because of lack of stock.