What is the expected number of times the bug will land on $0$ before it lands on $4$ for the first time?

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A bug is walking a number line such that all numbers are nonnegative. The bug starts at $1$. When it lands on $0$, it goes back to $1$, but from any other number on the number line, it goes left or right with equal probability.

What is the expected number of times the bug will land on $0$ before it lands on $4$ for the first time?

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Shamelessly ripping off Adapting Mathmo123's method to answer the problem asked:

Let $\mu_k$ denote the expected number of visits to $0$ before the first visit to $4$ if we start at $k.$ Then $$\begin{eqnarray} \mu_4 &=& 0,\\ \mu_3 &=& \frac 12 \mu_2 + \frac 12 \mu_4,\\ \mu_2 &=& \frac 12 \mu_1 + \frac 12 \mu_3,\\ \mu_1 &=& \frac 12 \mu_0 + \frac 12 \mu_2, \ \mbox{and}\\ \mu_0 &=& 1 + \mu_1.\\ \end{eqnarray}$$ The first equation is due to the fact that we can't visit anything before visiting $4$ if we start at $4;$ the last is due to the fact that being at $0$ gives us one visit, and afterward we will certainly visit $1;$ every other case is based on the $\frac 12$ probability of visiting either of the adjacent numbers next.

Solve for $\mu_1.$

A slightly more interesting question is what is the expected number of visits to $0$ before the first visit to $N$ if the bug starts at $M.$ It turns out there is a nice simple answer to that question. Apply that answer to the case $N = 4, M = 1.$