A study has shown that the probability distribution of x, the numbers of customers in line(including the one being served, if any) at a checkout line counter in a dept store, is given by P(X=0)=0.25, P(X=1)=.25, P(X=2)=.20, P(X=3)=.20, and P(X≥4)=.10. Consider a newly arriving customer to the checkout line.

a) What is the probablility that this customer will not have to wait behind anyone?
b) What is the probability that this customer will have to whit behind at least one customer?
c) On average, behind how many other customers will the newly arriving customer have to wait?