80. Найдите значение выражения: 1) 4\frac{1}{5} \cdot \frac{7}{15} \cdot \frac{1}{3}; 3) (5\frac{8}{9}:1\frac{17}{36}+1\frac{1}{4}):4\frac{1}{5}; 2) 4\frac{1}{5}:(\frac{7}{15} \cdot \frac{1}{3}); 4) (2\frac{1}{4}+4\frac{5}{6}):3\frac{2}{5}-\frac{3}{4} \cdot \frac{3}{5}.

Решим примеры на действия с дробями.

1)

$$4\frac{1}{5} \cdot \frac{7}{15} \cdot \frac{1}{3} = \frac{21}{5} \cdot \frac{7}{15} \cdot \frac{1}{3} = \frac{7}{5} \cdot \frac{7}{5} \cdot \frac{1}{3} = \frac{49}{75}$$

Ответ: $$\frac{49}{75}$$

2)

$$4\frac{1}{5}:(\frac{7}{15} \cdot \frac{1}{3}) = \frac{21}{5}:(\frac{7}{45}) = \frac{21}{5} \cdot \frac{45}{7} = \frac{3}{1} \cdot \frac{9}{1} = 27$$

Ответ: 27

3)

$$(5\frac{8}{9}:1\frac{17}{36}+1\frac{1}{4}):4\frac{1}{5} = (\frac{53}{9}:\frac{53}{36}+\frac{5}{4}):\frac{21}{5} = (\frac{53}{9} \cdot \frac{36}{53}+\frac{5}{4}):\frac{21}{5} = (4+\frac{5}{4}):\frac{21}{5} = \frac{21}{4}:\frac{21}{5} = \frac{21}{4} \cdot \frac{5}{21} = \frac{5}{4} = 1\frac{1}{4}$$

Ответ: $$1\frac{1}{4}$$

4)

$$(2\frac{1}{4}+4\frac{5}{6}):3\frac{2}{5}-\frac{3}{4} \cdot \frac{3}{5} = (\frac{9}{4}+ \frac{29}{6}):\frac{17}{5} - \frac{9}{20} = (\frac{27+58}{12}):\frac{17}{5} - \frac{9}{20} = \frac{85}{12}:\frac{17}{5} - \frac{9}{20} = \frac{85}{12} \cdot \frac{5}{17} - \frac{9}{20} = \frac{5}{12} \cdot \frac{5}{1} - \frac{9}{20} = \frac{25}{12} - \frac{9}{20} = \frac{125 - 27}{60} = \frac{98}{60} = \frac{49}{30} = 1\frac{19}{30}$$

Ответ: $$1\frac{19}{30}$$