3. Вычислите: 1) \(\frac{2}{7} + \frac{3}{8}\); 2) \(\frac{5}{6} - \frac{4}{9}\); 3) \(3\frac{1}{8} + 2\frac{5}{6}\); 4) \(5\frac{11}{12} - 3\frac{7}{18}\)

1) \(\frac{2}{7} + \frac{3}{8} = \frac{2 \cdot 8 + 3 \cdot 7}{7 \cdot 8} = \frac{16 + 21}{56} = \frac{37}{56}\)

2) \(\frac{5}{6} - \frac{4}{9} = \frac{5 \cdot 3 - 4 \cdot 2}{18} = \frac{15 - 8}{18} = \frac{7}{18}\)

3) \(3\frac{1}{8} + 2\frac{5}{6} = 3 + 2 + \frac{1}{8} + \frac{5}{6} = 5 + \frac{1 \cdot 3 + 5 \cdot 4}{24} = 5 + \frac{3 + 20}{24} = 5 + \frac{23}{24} = 5\frac{23}{24}\)

4) \(5\frac{11}{12} - 3\frac{7}{18} = 5 - 3 + \frac{11}{12} - \frac{7}{18} = 2 + \frac{11 \cdot 3 - 7 \cdot 2}{36} = 2 + \frac{33 - 14}{36} = 2 + \frac{19}{36} = 2\frac{19}{36}\)

Ответ: 1) \(\frac{37}{56}\); 2) \(\frac{7}{18}\); 3) \(5\frac{23}{24}\); 4) \(2\frac{19}{36}\)