Customers at a gas station pay with a credit card (A), debit card (B), or cash (C). Assume that successive customers make independent choices, with P(A) = .5, P(B) = .2, and P(C) = .3.
a. Among the next 100 customers, what are the mean and variance of the number who pay with a debit card? Explain your reasoning.
b. Answer part (a) for the number among the 100 who don't pay with cash.