A study has shown that the probability distribution of X, the number of customers in line (including the one being served, if any) at a checkout counter in a department store, is given by P(X=0) = 0.25, P(X=1) = 0.25, P(X=2) = 0.20, P(X=3) = 0.20, P(X>=4) = 0.10. Consider a newly arriving customer to the checkout line.

What is the probability that this customer will have to wait behind at least one customer?