2. a) 1/4 + (-3/16); б) 3/4 + 2/5; в) 5/36 + 5/27

a) \(\frac{1}{4} + \left(-\frac{3}{16}\right) = \frac{1\cdot4}{4\cdot4} - \frac{3}{16} = \frac{4}{16} - \frac{3}{16} = \frac{1}{16}\) б) \(\frac{3}{4} + \frac{2}{5} = \frac{3\cdot5}{4\cdot5} + \frac{2\cdot4}{5\cdot4} = \frac{15}{20} + \frac{8}{20} = \frac{23}{20}\) в) \(\frac{5}{36} + \frac{5}{27} = \frac{5\cdot3}{36\cdot3} + \frac{5\cdot4}{27\cdot4} = \frac{15}{108} + \frac{20}{108} = \frac{35}{108}\)