回復 25# yinyu222 的帖子
\(
\begin{array}{l}
先算兩人猜到最後分出勝負的期望值 \displaystyle E = \frac{2}{3} \times 1 + \frac{1}{3} \times (E + 1),E = \frac{3}{2} \\
再算三人猜到最後分出勝負的期望值 \displaystyle E^' = \frac{1}{3} \times 1+\frac{1}{3} \times (E^'+1)+\frac{1}{3} \times (E+1),E^' =\frac{9}{4} \\
\end{array}
\)