2) (13 2/7 : 31/70 - 28,5) : 6,75 + 20 2/3 - 19 9/10

Решение:

2. Второй пример:

1. \( 13\frac{2}{7} = \frac{93}{7} \)
2. \( \frac{93}{7} : \frac{31}{70} = \frac{93}{7} \cdot \frac{70}{31} = 3 \cdot 10 = 30 \)
3. \( 30 - 28,5 = 1,5 \)
4. \( 1,5 : 6,75 = \frac{15}{10} : \frac{675}{100} = \frac{3}{2} \cdot \frac{100}{675} = \frac{3}{1} \cdot \frac{50}{675} = \frac{150}{675} = \frac{2}{9} \)
5. \( 20\frac{2}{3} = \frac{62}{3} \)
6. \( 19\frac{9}{10} = \frac{199}{10} \)
7. \( \frac{2}{9} + \frac{62}{3} - \frac{199}{10} = \frac{2}{9} + \frac{186}{9} - \frac{199}{10} = \frac{188}{9} - \frac{199}{10} = \frac{1880 - 1791}{90} = \frac{89}{90} \)

Ответ: 89/90