3. Вычислите: а) $$\frac{3}{11} + \frac{5}{11}$$; б) $$\frac{2}{3} - \frac{3}{5}$$; в) $$\frac{7}{16} + \frac{1}{2}$$; г) $$\frac{5}{12} - \frac{2}{15}$$

а) $$\frac{3}{11} + \frac{5}{11} = \frac{3+5}{11} = \frac{8}{11}$$ б) $$\frac{2}{3} - \frac{3}{5} = \frac{2 \cdot 5}{3 \cdot 5} - \frac{3 \cdot 3}{5 \cdot 3} = \frac{10}{15} - \frac{9}{15} = \frac{10-9}{15} = \frac{1}{15}$$ в) $$\frac{7}{16} + \frac{1}{2} = \frac{7}{16} + \frac{1 \cdot 8}{2 \cdot 8} = \frac{7}{16} + \frac{8}{16} = \frac{7+8}{16} = \frac{15}{16}$$ г) $$\frac{5}{12} - \frac{2}{15} = \frac{5 \cdot 5}{12 \cdot 5} - \frac{2 \cdot 4}{15 \cdot 4} = \frac{25}{60} - \frac{8}{60} = \frac{25-8}{60} = \frac{17}{60}$$