a)
[tex]( \frac{2}{7} + \frac{5}{7} ) - \frac{2}{3 } = 1 - \frac{2}{3} = \frac{3 - 2}{3} = \frac{1}{3} [/tex]
b)
[tex] (\frac{2 \times 5 + 1}{5} \times \frac{3}{7}) \div \frac{11}{7} = (\frac{11}{5} \times \frac{3}{7} ) \div \frac{11}{7} = \frac{33}{35} \times \frac{7}{11} = \frac{3}{5} [/tex]
