Решение:

1. a) $$\frac{x}{2} + \frac{y}{3} = \frac{3x}{6} + \frac{2y}{6} = \frac{3x + 2y}{6}$$
2. б) $$\frac{c}{4} - \frac{d}{12} = \frac{3c}{12} - \frac{d}{12} = \frac{3c - d}{12}$$
3. в) $$\frac{a}{b^2} - \frac{b}{a} = \frac{a^2}{ab^2} - \frac{b^3}{ab^2} = \frac{a^2 - b^3}{ab^2}$$
4. г) $$\frac{3}{2x} - \frac{2}{3x} = \frac{9}{6x} - \frac{4}{6x} = \frac{9 - 4}{6x} = \frac{5}{6x}$$
5. д) $$\frac{5x}{8y} + \frac{x}{4y} = \frac{5x}{8y} + \frac{2x}{8y} = \frac{5x + 2x}{8y} = \frac{7x}{8y}$$
6. e) $$\frac{17y}{24c} - \frac{25y}{36c} = \frac{17y \cdot 3}{24c \cdot 3} - \frac{25y \cdot 2}{36c \cdot 2} = \frac{51y}{72c} - \frac{50y}{72c} = \frac{51y - 50y}{72c} = \frac{y}{72c}$$
7. ж) $$\frac{1}{5a} - \frac{8}{25a} = \frac{5}{25a} - \frac{8}{25a} = \frac{5 - 8}{25a} = \frac{-3}{25a} = -\frac{3}{25a}$$
8. з) $$\frac{3b}{4c} + \frac{c}{2b} = \frac{3b \cdot b}{4c \cdot b} + \frac{c \cdot 2c}{2b \cdot 2c} = \frac{3b^2}{4bc} + \frac{2c^2}{4bc} = \frac{3b^2 + 2c^2}{4bc}$$