Решение:

a) $$\frac{4y-1}{5y} - \frac{2y-7}{5y} + \frac{3y-1}{5y} = \frac{(4y-1) - (2y-7) + (3y-1)}{5y} = \frac{4y - 1 - 2y + 7 + 3y - 1}{5y} = \frac{5y + 5}{5y} = \frac{5(y+1)}{5y} = \frac{y+1}{y}$$

Ответ: $$\frac{y+1}{y}$$

б) $$\frac{7x-3}{4x} - \frac{x-4}{4x} - \frac{5-2x}{4x} = \frac{(7x-3) - (x-4) - (5-2x)}{4x} = \frac{7x - 3 - x + 4 - 5 + 2x}{4x} = \frac{8x - 4}{4x} = \frac{4(2x-1)}{4x} = \frac{2x-1}{x}$$

Ответ: $$\frac{2x-1}{x}$$

в) $$\frac{a-8}{a^2-25} + \frac{13}{a^2-25} = \frac{a-8+13}{a^2-25} = \frac{a+5}{a^2-25} = \frac{a+5}{(a-5)(a+5)} = \frac{1}{a-5}$$

Ответ: $$\frac{1}{a-5}$$