A clinic is staffed by two physicians who worked sequentially. The rst works from time 0 to time t1, and the second works from time tl to time t2 independently of the first. Patients arrive at the clinic following a Poisson distribution with parameter lambda per unit time. Given the total number of patients seen in the time interval (0, t2) is 11, nd the probability distribution of the total number of patients seen by physician 1