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我的想法是這樣...有錯不吝指導!
\(\matrix{1&2&3&4 \cr ⭕&✖&⭕&✖}\),5前面有2人中,\(\displaystyle \frac{3}{10}\times \frac{2}{9}\times \frac{7}{8}\times \frac{6}{7} \cdot C_2^4\)

\(\matrix{1&2&3&4 \cr ✖&✖&⭕&✖}\),5前面有1人中,\(\displaystyle \frac{3}{10}\times \frac{7}{9}\times \frac{6}{8}\times \frac{5}{7} \cdot C_1^4\)

\(\matrix{1&2&3&4 \cr ✖&✖&✖&✖}\),5前面有0人中,\(\displaystyle \frac{7}{10}\times \frac{6}{9}\times \frac{5}{8}\times \frac{4}{7} \cdot 1\)

\(\frac{\displaystyle \frac{3}{10}\times \frac{2}{9}\times \frac{7}{8}\times \frac{6}{7}\cdot C_2^3+
\frac{3}{10}\times\frac{7}{9}\times\frac{6}{8}\times\frac{5}{7}\cdot 1}{\displaystyle \frac{3}{10}\times \frac{2}{9}\times \frac{7}{8}\times \frac{6}{7} \cdot C_2^4+\frac{3}{10}\times \frac{7}{9}\times \frac{6}{8}\times \frac{5}{7} \cdot C_1^4+\frac{7}{10}\times \frac{6}{9}\times \frac{5}{8}\times \frac{4}{7} \cdot 1}\)

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