Solution

ID: past-exam-of-the-probability-statistics-and-options-ii-course-of-the-university-of-oxford/2011/m/m5/b/ii/solution

Write and propose , for . These probabilities sum to one because .
For , the incoming stationary probability is
using the telescoping identity . Similarly . Thus is stationary.
The finite chain is irreducible: every state can reach , and from every state is reachable in one step. Its self-loop at makes it aperiodic. The finite-state convergence theorem therefore gives the claimed limit from any initial state:
For this is the single absorbing refill state and the same formula gives probability one.

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