80. Найдите значение выражения: 1) 2 1/4 : 3/8 ⋅ 1/2 2) 2 1/4 : (3/8 : 1/2) 3) (6 3/4 - 5 1/8 : 1 9/32) ⋅ 2 1/5 4) (3 1/4 + 2 1/6) : 2 3/5 - 2/3 ⋅ 4/9

1. 1) \[ 2 \frac{1}{4} : \frac{3}{8} \cdot \frac{1}{2} = \frac{9}{4} : \frac{3}{8} \cdot \frac{1}{2} = \frac{9}{4} \cdot \frac{8}{3} \cdot \frac{1}{2} = \frac{9 \cdot 8 \cdot 1}{4 \cdot 3 \cdot 2} = \frac{3 \cdot 2 \cdot 1}{1 \cdot 1 \cdot 1} = 6 \]

2. 2) \[ 2 \frac{1}{4} : (\frac{3}{8} : \frac{1}{2}) = \frac{9}{4} : (\frac{3}{8} \cdot \frac{2}{1}) = \frac{9}{4} : \frac{3 \cdot 2}{8 \cdot 1} = \frac{9}{4} : \frac{3}{4} = \frac{9}{4} \cdot \frac{4}{3} = \frac{9 \cdot 4}{4 \cdot 3} = \frac{3 \cdot 1}{1 \cdot 1} = 3 \]

3. 3) \[ (6 \frac{3}{4} - 5 \frac{1}{8} : 1 \frac{9}{32}) \cdot 2 \frac{1}{5} = (\frac{27}{4} - \frac{41}{8} : \frac{41}{32}) \cdot \frac{11}{5} = (\frac{27}{4} - \frac{41}{8} \cdot \frac{32}{41}) \cdot \frac{11}{5} = (\frac{27}{4} - \frac{1}{1} \cdot \frac{4}{1}) \cdot \frac{11}{5} = (\frac{27}{4} - 4) \cdot \frac{11}{5} = (\frac{27}{4} - \frac{16}{4}) \cdot \frac{11}{5} = \frac{11}{4} \cdot \frac{11}{5} = \frac{121}{20} = 6 \frac{1}{20} \]

4. 4) \[ (3 \frac{1}{4} + 2 \frac{1}{6}) : 2 \frac{3}{5} - \frac{2}{3} \cdot \frac{4}{9} = (\frac{13}{4} + \frac{13}{6}) : \frac{13}{5} - \frac{2}{3} \cdot \frac{4}{9} = (\frac{39}{12} + \frac{26}{12}) : \frac{13}{5} - \frac{2}{3} \cdot \frac{4}{9} = \frac{65}{12} : \frac{13}{5} - \frac{2}{3} \cdot \frac{4}{9} = \frac{65}{12} \cdot \frac{5}{13} - \frac{2}{3} \cdot \frac{4}{9} = \frac{65 \cdot 5}{12 \cdot 13} - \frac{2 \cdot 4}{3 \cdot 9} = \frac{5 \cdot 5}{12 \cdot 1} - \frac{8}{27} = \frac{25}{12} - \frac{8}{27} = \frac{25 \cdot 9}{12 \cdot 9} - \frac{8 \cdot 4}{27 \cdot 4} = \frac{225}{108} - \frac{32}{108} = \frac{193}{108} = 1 \frac{85}{108} \]

Ответ: 1) 6; 2) 3; 3) \[6 \frac{1}{20}\]; 4) \[1 \frac{85}{108}\]