1. Найдите значение выражения 4,4 : (2,56 + 2,94).

1. $4,4 : (2,56 + 2,94) = 4,4 : 5,5 = 0,8$ 2. $\frac{7}{10} : (\frac{3}{8} - \frac{1}{5}) = \frac{7}{10} : (\frac{15-8}{40}) = \frac{7}{10} : \frac{7}{40} = \frac{7}{10} \cdot \frac{40}{7} = 4$ 3. $1\frac{5}{6} : (\frac{5}{12} - 1\frac{1}{3}) = \frac{11}{6} : (\frac{5}{12} - \frac{16}{12}) = \frac{11}{6} : (-\frac{11}{12}) = \frac{11}{6} \cdot (-\frac{12}{11}) = -2$ 4. $5,1 : (0,61 - 3,61) = 5,1 : (-3) = -1,7$ 5. $7,5 : (3,54 + 2,46) = 7,5 : 6 = 1,25$ 6. $32 \cdot (\frac{15}{16} - \frac{1}{8}) = 32 \cdot (\frac{15-2}{16}) = 32 \cdot \frac{13}{16} = 2 \cdot 13 = 26$ 7. $1\frac{2}{3} \cdot \frac{14}{25} : 1\frac{1}{6} = \frac{5}{3} \cdot \frac{14}{25} \cdot \frac{6}{7} = \frac{5 \cdot 14 \cdot 6}{3 \cdot 25 \cdot 7} = \frac{1 \cdot 2 \cdot 2}{1 \cdot 5 \cdot 1} = \frac{4}{5} = 0,8$ 8. $(1,68 + 1,82) \cdot 1,8 = 3,5 \cdot 1,8 = 6,3$ 9. $1\frac{1}{2} \cdot \frac{5}{12} : 1\frac{1}{4} = \frac{3}{2} \cdot \frac{5}{12} \cdot \frac{4}{5} = \frac{3 \cdot 5 \cdot 4}{2 \cdot 12 \cdot 5} = \frac{60}{120} = \frac{1}{2} = 0,5$ 10. $(1,84 + 0,96) \cdot 3,5 = 2,8 \cdot 3,5 = 9,8$ 11. $4 + 8x - 5x^2 = 0$ $5x^2 - 8x - 4 = 0$ $D = (-8)^2 - 4 \cdot 5 \cdot (-4) = 64 + 80 = 144$ $x_1 = \frac{8 + 12}{10} = 2$; $x_2 = \frac{8 - 12}{10} = -0,4$ 12. $10(x - 9) = 7$ $10x - 90 = 7$ $10x = 97$ $x = 9,7$