12. Вычислим:$$1\frac{4}{9} : \frac{16}{27} = \frac{1 \cdot 9 + 4}{9} : \frac{16}{27} = \frac{9+4}{9} : \frac{16}{27} = \frac{13}{9} : \frac{16}{27} = \frac{13}{9} \cdot \frac{27}{16} = \frac{13 \cdot 27}{9 \cdot 16} = \frac{13 \cdot 3 \cdot 9}{9 \cdot 16} = \frac{13 \cdot 3}{16} = \frac{39}{16} = 2\frac{7}{16}$$
Ответ: 2\frac{7}{16}