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Let \(\{X_{n}\}_{0}^{\infty}\) be a Markov chain with \(P[X_{0} = 0] = P[X_{0} = 1] = \dfrac{1}{4}\) and \(P[X_{0} = 2] = \dfrac{1}{2}\). The t.p.m. is given by :

012
01/21/31/6
101/32/3
21/201/2

Then \(P[X_{1} = 1]\) is given by :

  • A.\(\dfrac{1}{3}\)
  • B.\(\dfrac{1}{4}\)
  • C.\(\dfrac{1}{5}\)
  • D.\(\dfrac{1}{6}\)

Answer: D

\(P[X_{1} = 1] = \) 1/6.

Multiply the initial distribution by the column of the transition matrix for state 1:

\[ \begin{aligned} P[X_{1} = 1] &= \tfrac{1}{4}\cdot\tfrac{1}{3} + \tfrac{1}{4}\cdot\tfrac{1}{3} + \tfrac{1}{2}\cdot 0 \\ &= \tfrac{1}{12} + \tfrac{1}{12} = \tfrac{1}{6} \end{aligned} \]

1/3 is just the transition probability from 0 (or 1) to 1, ignoring the starting distribution, and 1/4 is the initial probability of state 1.

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