Найдите значение выражения:
а) $(1 - \frac{3}{4}) * (\frac{4}{5} - \frac{3}{4})$;
б) $14 * (\frac{1}{2} + \frac{1}{3} + \frac{1}{4})$;
в) $\frac{1}{3} * \frac{6}{7} - \frac{1}{7} * \frac{3}{4}$.
$(1 - \frac{3}{4}) * (\frac{4}{5} - \frac{3}{4}) = \frac{1}{4} * (\frac{16}{20} - \frac{15}{20}) = \frac{1}{4} * \frac{1}{20} = \frac{1}{80}$
$14 * (\frac{1}{2} + \frac{1}{3} + \frac{1}{4}) = 14 * (\frac{6}{12} + \frac{4}{12} + \frac{3}{12}) = 14 * \frac{13}{12} = 7 * \frac{13}{6} = \frac{91}{6} = 15\frac{1}{6}$
$\frac{1}{3} * \frac{6}{7} - \frac{1}{7} * \frac{3}{4} = \frac{1}{1} * \frac{2}{7} - \frac{3}{28} = \frac{8}{28} - \frac{3}{28} = \frac{5}{28}$