86. Выполните действие: a) $$\frac{4}{5}+\frac{2}{3}$$; б) $$\frac{7}{8}-\frac{11}{12}$$; в) $$\frac{3}{10}+2\frac{1}{5}$$; г) $$5\frac{3}{14}-1\frac{1}{21}$$

Решение:

1. \(\frac{4}{5}+\frac{2}{3} = \frac{12}{15}+\frac{10}{15} = \frac{22}{15}\)
2. \(\frac{7}{8}-\frac{11}{12} = \frac{21}{24}-\frac{22}{24} = -\frac{1}{24}\)
3. \(\frac{3}{10}+2\frac{1}{5} = \frac{3}{10}+\frac{11}{5} = \frac{3}{10}+\frac{22}{10} = \frac{25}{10} = \frac{5}{2}\)
4. \(5\frac{3}{14}-1\frac{1}{21} = \frac{73}{14}-\frac{22}{21} = \frac{219}{42}-\frac{44}{42} = \frac{175}{42} = \frac{25}{6}\)

Ответ: а) $$\frac{22}{15}$$; б) $$-\frac{1}{24}$$; в) $$\frac{5}{2}$$; г) $$\frac{25}{6}$$.