Ответ:

  1. \( -9.6 : 12 - 29 : (-5.8) + 4 : (-25) \)

    \(= -0.8 - (-5) - 0.16 = 4.04\).

  2. \( -3.4 : (4 - 4.6) + 12.4 \cdot (-0.8 - 2.2) \)

    \(= -3.4 : (-0.6) + 12.4 \cdot (-3)\)

    \(= \frac{17}{3} - 37.2 = \frac{17}{3} - \frac{186}{5} = -\frac{473}{15} = -31\frac{8}{15}\).

  3. \( (0.4 - \frac{3}{20}) \cdot 6\frac{2}{3} - 1.75 : (-7\frac{7}{8}) \)

    \(= (\frac{2}{5} - \frac{3}{20}) \cdot \frac{20}{3} - \frac{7}{4} : (-\frac{63}{8})\)

    \(= \frac{1}{4} \cdot \frac{20}{3} + \frac{2}{9} = \frac{5}{3} + \frac{2}{9} = \frac{17}{9}\).

  4. \( (6.3 : (-\frac{9}{20}) - 2.6 : (-\frac{1}{20})) \cdot (-\frac{4}{19}) \)

    \(= (-14 - (-52)) \cdot (-\frac{4}{19})\)

    \(= 38 \cdot (-\frac{4}{19}) = -8\).

Ответ: 1) 4,04; 2) \(-31\frac{8}{15}\); 3) \(\frac{17}{9}\); 4) −8.