3. Выполните a) 8/15 - 4/15 + 1/15 ; б) 5/6 + 3/8 ; в) 7/12 - 7/20 ; г) 5 5/6 + 6 3/4 ;

а) $$\frac{8}{15} - \frac{4}{15} + \frac{1}{15} = \frac{8 - 4 + 1}{15} = \frac{5}{15} = \frac{1}{3}$$

Ответ: $$\frac{1}{3}$$

б) $$\frac{5}{6} + \frac{3}{8} = \frac{5 \cdot 4}{6 \cdot 4} + \frac{3 \cdot 3}{8 \cdot 3} = \frac{20}{24} + \frac{9}{24} = \frac{20 + 9}{24} = \frac{29}{24} = 1 \frac{5}{24}$$

Ответ: $$1 \frac{5}{24}$$

в) $$\frac{7}{12} - \frac{7}{20} = \frac{7 \cdot 5}{12 \cdot 5} - \frac{7 \cdot 3}{20 \cdot 3} = \frac{35}{60} - \frac{21}{60} = \frac{35 - 21}{60} = \frac{14}{60} = \frac{7}{30}$$

Ответ: $$\frac{7}{30}$$

г) $$5 \frac{5}{6} + 6 \frac{3}{4} = 5 + \frac{5}{6} + 6 + \frac{3}{4} = 11 + \frac{5 \cdot 2}{6 \cdot 2} + \frac{3 \cdot 3}{4 \cdot 3} = 11 + \frac{10}{12} + \frac{9}{12} = 11 + \frac{10 + 9}{12} = 11 + \frac{19}{12} = 11 + 1 \frac{7}{12} = 12 \frac{7}{12}$$

Ответ: $$12 \frac{7}{12}$$