5) 9 7/9 - 4 5/6 ;

5) $$9 \frac{7}{9} - 4 \frac{5}{6} = (9 - 4) + (\frac{7}{9} - \frac{5}{6}) = 5 + (\frac{7 \cdot 2}{9 \cdot 2} - \frac{5 \cdot 3}{6 \cdot 3}) = 5 + (\frac{14}{18} - \frac{15}{18}) = 5 - \frac{1}{18} = 4 \frac{18}{18} - \frac{1}{18} = 4 \frac{17}{18}$$

Ответ: $$4 \frac{17}{18}$$