Tính nhanh:

a) $\frac{{6 \times 7 \times 8 \times 9 \times 10 \times 11}}{{22 \times 20 \times 18 \times 16 \times 14 \times 12}}$

b) $\left( {1 - \frac{1}{2}} \right) \times \left( {1 - \frac{1}{3}} \right) \times \left( {1 - \frac{1}{4}} \right) \times \left( {1 - \frac{1}{5}} \right) \times \left( {1 - \frac{1}{6}} \right)$

a) $\frac{{6 \times 7 \times 8 \times 9 \times 10 \times 11}}{{22 \times 20 \times 18 \times 16 \times 14 \times 12}}$

$= \frac{{6 \times 7 \times 8 \times 9 \times 10 \times 11}}{{11 \times 2 \times 10 \times 2 \times 9 \times 2 \times 8 \times 2 \times 7 \times 2 \times 6 \times 2}}$

$= \frac{1}{{2 \times 2 \times 2 \times 2 \times 2 \times 2}}$

$= \frac{1}{{64}}$

b) $\left( {1 - \frac{1}{2}} \right) \times \left( {1 - \frac{1}{3}} \right) \times \left( {1 - \frac{1}{4}} \right) \times \left( {1 - \frac{1}{5}} \right) \times \left( {1 - \frac{1}{6}} \right)$

$= \frac{1}{2} \times \frac{2}{3} \times \frac{3}{4} \times \frac{4}{5} \times \frac{5}{6}$

$= \frac{1}{6}$