Điền số thích hợp vào dấu “...”:

a) \(\frac{3}{7} = \frac{{...}}{{21}}\);            b) \(\frac{{...}}{9} = \frac{{32}}{{72}}\);                c) \(\frac{{44}}{{77}} = \frac{4}{{...}}\);               d) \(\frac{9}{{...}} = \frac{{81}}{{81}}\);

Hướng Dẫn Giải

\(13 = \frac{{13}}{1} = \frac{{13 \times 3}}{{1 \times 3}} = \frac{{39}}{3}\);                        \(13 = \frac{{13}}{1} = \frac{{13 \times 5}}{{1 \times 5}} = \frac{{65}}{5}\);

\(13 = \frac{{13}}{1} = \frac{{13 \times 10}}{{1 \times 10}} = \frac{{130}}{{10}}\);                            \(13 = \frac{{13}}{1} = \frac{{13 \times 17}}{{1 \times 17}} = \frac{{221}}{{17}}\);

Hướng Dẫn Giải

\(\frac{5}{7} = \frac{{5 \times 2}}{{7 \times 2}} = \frac{{10}}{{14}}\);                              \(\frac{5}{7} = \frac{{5 \times 4}}{{7 \times 4}} = \frac{{20}}{{28}}\);

\(\frac{5}{7} = \frac{{5 \times 5}}{{7 \times 5}} = \frac{{25}}{{35}}\);                              \(\frac{5}{7} = \frac{{5 \times 15}}{{7 \times 15}} = \frac{{75}}{{105}}\);