Lời giải:
\(\frac{11}{2}.\frac{12}{2}.\frac{13}{2}....\frac{20}{2}=\frac{(12.14.16.18.20)(11.13.15.17.19)}{2^{10}}\)
\(=\frac{12}{2^2}.\frac{14}{2}.\frac{16}{2^4}.\frac{18}{2}.\frac{20}{2^2}(11.13.15.17.19)\)
\(=3.7.1.9.5.11.13.15.17.19=1.3.5.7.9.11.13.15.17.19\)