\[\boxed{\text{П.17.}}\]
\[\textbf{а)}\ \frac{1}{3} + \frac{1}{2} = \frac{2 + 3}{6} = \frac{5}{6}\ \]
\[\textbf{б)}\ \frac{2}{5} + \frac{3}{10} = \frac{2 \cdot 2 + 3}{10} = \frac{7}{10}\ \]
\[\textbf{в)}\ \frac{7}{8} - \frac{3}{16} = \frac{7 \cdot 2 - 3}{16} = \frac{11}{16}\ \]
\[\textbf{г)}\ \frac{11}{12} - \frac{3}{4} = \frac{11 - 3 \cdot 3}{12} = \frac{2}{12} = \frac{1}{6}\ \]
\[\textbf{д)}\ \frac{4}{15} + \frac{3}{12} = \frac{4 \cdot 4 + 3 \cdot 5}{60} =\]
\[= \frac{16 + 15}{60} = \frac{31}{60}\ \]
\[\textbf{е)}\ \frac{2}{9} + \frac{11}{15} = \frac{2 \cdot 5 + 11 \cdot 3}{45} =\]
\[= \frac{10 + 33}{45} = \frac{43}{45}\text{\ \ \ }\]