A supermarket has two customers waiting to pay for their purchases at counter I and one customer waiting to pay at counter II. Let Y1 and Y2 denote the numbers of customers who spend more than $50 on groceries at the respective counters. Suppose that Y1 and Y2 are independent binomial random variables, with the probability that a customer at counter I will spend more than $50 equal to .2 and the probability that a customer at counter II will spend more than $50 equal to .3. Find the

a joint probability distribution for Y1 and Y2.

b probability that not more than one of the three customers will spend more than $50.