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) = 0.5, P(B) = 0.2, and P(C) = 0.3. (a) Among the next 100 customers, what are the mean and variance of the number who pay with a debit card? (b) Answer part (a) for the number among the 100 who don't pay with cash.