a) \(1 - \frac{1}{2} + \frac{1}{3} = \frac{6 - 3 + 2}{6} = \frac{5}{6}\).

b) \(\frac{2}{5} + \frac{3}{5} : \frac{9}{10} = \frac{2}{5} + \frac{3}{5} \cdot \frac{10}{9} = \frac{2}{5} + \frac{2}{3} = \frac{16}{15}\).

c) \(\frac{7}{11} \cdot \frac{3}{4} + \frac{7}{11} \cdot \frac{1}{4} + \frac{4}{11} = \frac{7}{11} \left(\right. \frac{3}{4} + \frac{1}{4} \left.\right) + \frac{4}{11} = \frac{7}{11} + \frac{4}{11} = 1\).

d) \(\left(\right. \frac{3}{4} + 0 , 5 + 25 \% \left.\right) \cdot 2 \frac{2}{3} = \left(\right. \frac{3}{4} + \frac{1}{2} + \frac{1}{4} \left.\right) \cdot \frac{8}{3} = \frac{3}{2} \cdot \frac{8}{3} = 4\).