[math] \newcommand{\NA}{{\rm NA}} \newcommand{\mat}[1]{{\bf#1}} \newcommand{\exref}[1]{\ref{##1}} \newcommand{\secstoprocess}{\all} \newcommand{\NA}{{\rm NA}} \newcommand{\mathds}{\mathbb}[/math]

In the game in Exercise, let [math]p = q = 1/2[/math] and [math]M = 10[/math]. What is the probability that the gambler's stake equals [math]M[/math] at least 20 times before it returns to 0?