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

Of all customers purchasing automatic garage door openers, 75% purchase chain-driven model.
Let X = the number among the next 15 purchasers who select the chain-driven model.
a. What is the frequency function (pmf) of X?
b. Compute P(X > 10).
c. Compute P( 6 ≤ X ≤ 10).
d. Compute µ and σ2
e. If the store currently has in stock 10 chain-driven models and 8 shaft-driven models, what is the
probability that at least 7 out of the 15 customers select a chain-driven model from this stock?