Решение:

1. a) $$rac{5}{24} - \frac{1}{6} = \frac{5}{24} - \frac{4}{24} = \frac{1}{24}$$

2. б) $$2\frac{1}{3} : (-7) = \frac{7}{3} : (-7) = \frac{7}{3} \cdot (-\frac{1}{7}) = -\frac{1}{3}$$

3. в) $$0,03 \cdot \frac{1}{3} = \frac{3}{100} \cdot \frac{1}{3} = \frac{1}{100} = 0,01$$

4. г) $$0,21 : \frac{7}{9} = \frac{21}{100} : \frac{7}{9} = \frac{21}{100} \cdot \frac{9}{7} = \frac{3}{100} \cdot 9 = \frac{27}{100} = 0,27$$

Проверьте, верно ли равенство:

8,16 * (-0,5) + 5 = 1,92

8,16 * (-0,5) + 5 = -4,08 + 5 = 0,92 ≠ 1,92