(2 1per8-1 3per4):(3 5per6-4 1per4)

[tex](2 \frac{1}{8} - 1 \frac{3}{4} ) \div (3 \frac{5}{6} - 4 \frac{1}{4} ) \\ = ( \frac{17}{8} - \frac{7}{4} ) \div ( \frac{23}{6} - \frac{17}{4} ) \\ = ( \frac{17}{8} - \frac{14}{8} ) \div ( \frac{46}{12} - \frac{51}{12} ) \\ = \frac{3}{8} \div ( - \frac{5}{12} ) \\ = \frac{3}{8} \times ( - \frac{12}{5} ) \\ = - \frac{36}{40} \\ = - \frac{9}{10} [/tex]