APPLICATIONS 3. A certain cereal comes in three box sizes. At Sally's Supermarket, 20% of the sales are 20 oz. boxes, 50% are 23 oz. boxes, and 30% are 26 oz. boxes. Let X be the number of ounces in the next box of this cereal purchased at Sally's. We know: E[X] = 23.3 and SD(X) = 2.1. a) Write the pmf of X. b) Find the Z-score of a 20 oz. box.