5.15 Найдите значение выражения: a) $$2\frac{3}{6} + 3\frac{5}{9} - 6\frac{3}{12}$$; б) $$4\frac{1}{4} - 3\frac{2}{3} - 2\frac{7}{8}$$; в) $$4\frac{1}{6} - 9\frac{4}{9} + 3\frac{7}{12}$$; г) $$7\frac{1}{5} - 4\frac{2}{15} - 9\frac{2}{3}$$.

a) $$2\frac{3}{6} + 3\frac{5}{9} - 6\frac{3}{12} = 2\frac{1}{2} + 3\frac{5}{9} - 6\frac{1}{4} = \frac{5}{2} + \frac{32}{9} - \frac{25}{4} = \frac{90}{36} + \frac{128}{36} - \frac{225}{36} = \frac{90 + 128 - 225}{36} = \frac{218 - 225}{36} = \frac{-7}{36}$$. б) $$4\frac{1}{4} - 3\frac{2}{3} - 2\frac{7}{8} = \frac{17}{4} - \frac{11}{3} - \frac{23}{8} = \frac{102}{24} - \frac{88}{24} - \frac{69}{24} = \frac{102 - 88 - 69}{24} = \frac{14 - 69}{24} = \frac{-55}{24} = -2\frac{7}{24}$$. в) $$4\frac{1}{6} - 9\frac{4}{9} + 3\frac{7}{12} = \frac{25}{6} - \frac{85}{9} + \frac{43}{12} = \frac{150}{36} - \frac{340}{36} + \frac{129}{36} = \frac{150 - 340 + 129}{36} = \frac{-190 + 129}{36} = \frac{-61}{36} = -1\frac{25}{36}$$. г) $$7\frac{1}{5} - 4\frac{2}{15} - 9\frac{2}{3} = \frac{36}{5} - \frac{62}{15} - \frac{29}{3} = \frac{108}{15} - \frac{62}{15} - \frac{145}{15} = \frac{108 - 62 - 145}{15} = \frac{46 - 145}{15} = \frac{-99}{15} = -\frac{33}{5} = -6\frac{3}{5}$$. Ответ: a) $$-\frac{7}{36}$$; б) $$-2\frac{7}{24}$$; в) $$-1\frac{25}{36}$$; г) $$-6\frac{3}{5}$$.