Найдите значение выражения:
а) $(1 - \frac{1}{2}) : (\frac{1}{2} - \frac{1}{3})$;
б) $(\frac{1}{3} + \frac{1}{4}) : (2 - \frac{5}{6})$;
в) $(\frac{1}{2} + \frac{1}{4} - \frac{2}{5}) : \frac{4}{5}$.
$(1 - \frac{1}{2}) : (\frac{1}{2} - \frac{1}{3}) = \frac{1}{2} : (\frac{3}{6} - \frac{2}{6}) = \frac{1}{2} : \frac{1}{6} = \frac{1}{2} * \frac{6}{1} = \frac{1}{1} * \frac{3}{1} = 3$
$(\frac{1}{3} + \frac{1}{4}) : (2 - \frac{5}{6}) = (\frac{4}{12} + \frac{3}{12}) : 1\frac{1}{6} = \frac{7}{12} : \frac{7}{6} = \frac{7}{12} * \frac{6}{7} = \frac{1}{2} * \frac{1}{1} = \frac{1}{2}$
$(\frac{1}{2} + \frac{1}{4} - \frac{2}{5}) : \frac{4}{5} = (\frac{10}{20} + \frac{5}{20} - \frac{8}{20}) * \frac{5}{4} = \frac{7}{20} * \frac{5}{4} = \frac{7}{4} * \frac{1}{4} = \frac{7}{16}$