Given a transition matrix $$P(3X3) = \begin{pmatrix} 0.3& 0.7& 0\\
0.4 &0 & 0.6\\
0 &0.5& 0.5 \end{pmatrix}$$
Starting with level $0$ on the top left and moving down to level $2$ towards the bottom.
Question: If the person starts on level $0$ what is the probability they will not reach level $2$ once in the next four years?
I have tried multiple things such as calculating the probability of reaching level 2 at each year then multiplying those together and subtracting them from one but I don't get the right answer for any. Please help.
Best Answer
Here is the question I assume you are trying to ask:
Following an idea from the comments: if we make level 2 an absorbing state, i.e. if we replace the bottom row with $(0,0,1)$ to form the matrix $Q$, then the probability of reaching level 2 at some point is the $1,3$ entry of the matrix $Q^4$. That is, it is the $1,3$ entry of the matrix $Q^4$, where $$ Q = \pmatrix{0.3& 0.7& 0\\ 0.4 &0 & 0.6\\ 0 & 0 & 0.5}. $$ With a direct computation, we see that this probability is $0.7014$. It follows that the desired probability is equal to $1 - 0.7014 = 0.2986$.