$\text{a)}$  

$3\frac{1}{5}:3\frac{1}{3}:8=\frac{16}{5}:\frac{10}{3}:8=\frac{16}{5}\cdot \frac{3}{10}\cdot \frac{1}{8}=\frac{48}{50}\cdot \frac{1}{8}=\frac{6}{50}=\frac{3}{25}$  

$1\frac{1}{5}\cdot 2\frac{5}{8}:2\frac{1}{3}=\frac{6}{5}\cdot \frac{21}{8}:\frac{7}{3}=\frac{63}{20}\cdot \frac{3}{7}=\frac{27}{20}=1\frac{7}{20}$  

$10:1\frac{2}{3}\cdot 2\frac{3}{4}=10:\frac{5}{3}\cdot \frac{11}{4}=10\cdot \frac{3}{5}\cdot \frac{11}{4}=6\cdot \frac{11}{4}=\frac{33}{2}=16\frac{1}{2}$  

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$\text{b)}$  

$3\frac{1}{3}\cdot \frac{3}{4}:1\frac{2}{5}=\frac{10}{3}\cdot \frac{3}{4}:\frac{7}{5}=\frac{5}{2}\cdot \frac{5}{7}=\frac{25}{14}=1\frac{11}{14}$  

$2\frac{1}{4}:1\frac{1}{6}:\frac{9}{10}=\frac{9}{4}:\frac{7}{6}:\frac{9}{10}=\frac{9}{4}\cdot \frac{6}{7}\cdot \frac{10}{9}=\frac{60}{28}=\frac{15}{7}=2\frac{1}{7}$  

$2\frac{5}{8}:7\cdot 1\frac{1}{6}=\frac{21}{8}\cdot \frac{1}{7}\cdot \frac{7}{6}=\frac{21}{8}\cdot \frac{1}{6}=\frac{7}{16}$  

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$\text{c)}$  

$4\frac{1}{2}:1\frac{1}{8}-3\frac{5}{8}=\frac{9}{2}:\frac{9}{8}-3\frac{5}{8}=\frac{9}{2}\cdot \frac{8}{9}-3\frac{5}{8}=4-3\frac{5}{8}=3\frac{8}{8}-3\frac{5}{8}=\frac{3}{8}$  

$100-12\frac{2}{3}:\frac{5}{6}=100-\frac{38}{3}\cdot \frac{6}{5}=100-\frac{76}{5}=100-15\frac{1}{5}=99\frac{5}{5}-15\frac{1}{5}=84\frac{4}{5}$  

$18+\frac{23}{4}\cdot 2\frac{2}{3}=18+\frac{11}{4}\cdot \frac{8}{3}=18+\frac{22}{3}=18+7\frac{1}{3}=25\frac{1}{3}$