The rate a certain insurance company charges its policyholders alternates between r_{1} and r_{0}. A new policyholder is initially charged at a rate of r_{1} per unit time. When a policyholder paying at rate r_{1} has made no claims for the most recent s time units, then the rate charged becomes r_{0} per unit time. The rate charged remains at r_{0} until a claim is made, at which time it reverts to r_{1}. Suppose that a given policyholder lives forever and makes claims at times chosen according to a Poisson process with rate λ, and find
(a) P_{i} , the proportion of time that the policyholder pays at rate r_{i} , i = 0, 1;
(b) the long-run average amount paid per unit time.