A repairman services n machine of a certain type, which are all placed in one column, one next to each other. The distance between two successive machines is a. The repairman moves to the next machine after he finishes the repair of one machine and only if a new machine needs a repair. Assuming that each machine operates independently of any other machine and the probability of a machine failure is p>0, what is the average distance the repairman has to cover when he moves from one machine that he repaired to another. This problem is a bit challenging. I suggest that you use two random variables to solve it. What is the expected distance that the repairman has to cover if the repairman has just repaired the first machine in the column?