3. Вычислите: a) 2/13 + 1/3 б) 3/12 - 5/36 в) 2/3 + 3/20 + 4/59

а) \(\frac{2}{13} + \frac{1}{3} = \frac{6}{39} + \frac{13}{39} = \frac{19}{39}\) б) \(\frac{3}{12} - \frac{5}{36} = \frac{9}{36} - \frac{5}{36} = \frac{4}{36} = \frac{1}{9}\) в) \(\frac{2}{3} + \frac{3}{20} + \frac{4}{59} = \frac{2 \cdot 20 \cdot 59 + 3 \cdot 3 \cdot 59 + 4 \cdot 3 \cdot 20}{3 \cdot 20 \cdot 59} = \frac{2360 + 531 + 240}{3540} = \frac{3131}{3540}\)