Can you show me how to establish this formula in excel, along with the answer?
A small grocery store is considering installing an express checkout line. Let X be the number of customers in the regular checkout line. Note that these numbers include the customers being served, if any. The probability distribution of X is given in the table below.
x 0 1 2 3
P(X=x) 0.20 0.30 0.25 0.25
Find the probability that at most one customer is in the regular checkout line.