\[\boxed{\mathbf{984}\mathbf{.}\mathbf{\ }}\]
\[1)\ \frac{4}{9}\ и\ \frac{7}{12}\ \Longrightarrow \frac{16}{36}\ и\ \frac{21}{36}\]
\[2)\ \frac{3}{8}\ и\ \frac{4}{15} \Longrightarrow \frac{45}{120}\ и\ \frac{32}{120}\]
\[3)\ \frac{2}{15}\ и\ \frac{11}{12} \Longrightarrow \frac{8}{60}\ и\ \frac{55}{60}\]
\[4)\ \frac{3}{10};\ \ \frac{3}{8}\ и\ \ \frac{3}{4} \Longrightarrow \frac{12}{40};\ \ \frac{15}{40}\ и\ \frac{30}{40}\]