Rút gọn: Rút gọn: A = 7! .4!/ 10! ( 8! / 3!.5! - 6! / 2!4!)

\(A = \frac{{7! \cdot 4!}}{{10!}}\left( {\frac{{8!}}{{3!5!}} - \frac{{6!}}{{2!4!}}} \right) = \frac{{7!1 \cdot 2 \cdot 3 \cdot 4}}{{7! \cdot 8 \cdot 9 \cdot 10}}\left( {\frac{{5! \cdot 6 \cdot 7 \cdot 8}}{{1 \cdot 2 \cdot 3.5!}} - \frac{{4! \cdot 5 \cdot 6}}{{1.2.4!}}} \right) = \frac{1}{{30}}(56 - 15) = \frac{{41}}{{30}}\).