Of all customers purchasing automatic garage-door openers, 75% purchase a chain-driven model. Let number among the next 15 purchasers who select the chain-driven model.

a. What is the pmf of X?

b. Compute .

c. Compute .

d. Compute m and s2

.

e. If the store currently has in stock 10 chain-driven models and 8 shaft-driven models, what is the probability that the requests of these 15 customers can all be met from existing stock?