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

1. \(2\frac{1}{4}:\frac{3}{8}:\frac{1}{2}=\frac{9}{4}\cdot\frac{8}{3}\cdot2=12\).
2. \(2\frac{1}{4}:\left(\frac{3}{5}:\frac{1}{2}\right)=\frac{9}{4}:\frac{6}{5}=\frac{9}{4}\cdot\frac{5}{6}=\frac{15}{8}=1\frac{7}{8}\).
3. \(5\frac{1}{8}:1\frac{9}{32}=\frac{41}{8}:\frac{41}{32}=4\).
   \(6\frac{3}{4}-4=\frac{27}{4}-4=\frac{11}{4}\).
   \(\frac{11}{4}:2\frac{1}{6}=\frac{11}{4}:\frac{13}{6}=\frac{11}{4}\cdot\frac{6}{13}=\frac{33}{26}=1\frac{7}{26}\).
4. \(3\frac{1}{4}+2\frac{1}{6}=\frac{13}{4}+\frac{13}{6}=\frac{65}{12}\).
   \(\frac{65}{12}:2\frac{3}{5}=\frac{65}{12}:\frac{13}{5}=\frac{25}{12}\).
   \(\frac{2}{3}:\frac{4}{9}=\frac{3}{2}\).
   \(\frac{25}{12}-\frac{3}{2}=\frac{25}{12}-\frac{18}{12}=\frac{7}{12}\).

Ответ: 1) 12; 2) \(1\frac{7}{8}\); 3) \(1\frac{7}{26}\); 4) \(\frac{7}{12}\).