Viết tiếp vào chỗ chấm cho thích hợp:

a)\(\frac{4}{5} \times \frac{3}{7} = \frac{{4 \times 3}}{{5 \times 7}} = \frac{{12}}{{35}}\)

\(\frac{3}{7} \times \frac{4}{5} = \frac{{3 \times 4}}{{7 \times 5}} = \frac{{12}}{{35}}\)

b)\(\frac{2}{3} \times \frac{5}{7} = \frac{{2 \times 5}}{{3 \times 7}} = \frac{{10}}{{21}}\)

\(\frac{5}{7} \times \frac{2}{3} = \frac{{5 \times 2}}{{7 \times 3}} = \frac{{10}}{{21}}\)