1) 3/4 * 8/9; 2) 25 * 4/5; 3) (3/4)^2; 4) 7/9 * 0; 5) 4/5 : 2/25; 6) 10 : 2/5; 7) 2/5 : 10; 8) 3/7 : 3/7; 9) 0 : 3/7; 10) 3/7 : 0; 11) 1 : 3/7; 12) 3/7 : 1.

1) $\frac{3}{4} \cdot \frac{8}{9} = \frac{3 \cdot 8}{4 \cdot 9} = \frac{24}{36} = \frac{2}{3}$ 2) $25 \cdot \frac{4}{5} = \frac{25 \cdot 4}{5} = 5 \cdot 4 = 20$ 3) $(\frac{3}{4})^2 = \frac{3^2}{4^2} = \frac{9}{16}$ 4) $\frac{7}{9} \cdot 0 = 0$ 5) $\frac{4}{5} : \frac{2}{25} = \frac{4}{5} \cdot \frac{25}{2} = \frac{4 \cdot 25}{5 \cdot 2} = 2 \cdot 5 = 10$ 6) $10 : \frac{2}{5} = 10 \cdot \frac{5}{2} = \frac{10 \cdot 5}{2} = 5 \cdot 5 = 25$ 7) $\frac{2}{5} : 10 = \frac{2}{5} \cdot \frac{1}{10} = \frac{2}{50} = \frac{1}{25}$ 8) $\frac{3}{7} : \frac{3}{7} = 1$ 9) $0 : \frac{3}{7} = 0$ 10) $\frac{3}{7} : 0$ — на ноль делить нельзя 11) $1 : \frac{3}{7} = 1 \cdot \frac{7}{3} = \frac{7}{3} = 2\frac{1}{3}$ 12) $\frac{3}{7} : 1 = \frac{3}{7}$