а) $$\frac{1}{4} + \frac{1}{8} = \frac{1 \times 2}{4 \times 2} + \frac{1}{8} = \frac{2}{8} + \frac{1}{8} = \frac{2 + 1}{8} = \frac{3}{8}$$
Ответ: $$\frac{3}{8}$$
б) $$\frac{2}{3} - \frac{1}{6} = \frac{2 \times 2}{3 \times 2} - \frac{1}{6} = \frac{4}{6} - \frac{1}{6} = \frac{4 - 1}{6} = \frac{3}{6} = \frac{1}{2}$$
Ответ: $$\frac{1}{2}$$
в) $$\frac{3}{7} \times \frac{1}{3} = \frac{3 \times 1}{7 \times 3} = \frac{3}{21} = \frac{1}{7}$$
Ответ: $$\frac{1}{7}$$
г) $$\frac{4}{9} \div \frac{3}{7} = \frac{4}{9} \times \frac{7}{3} = \frac{4 \times 7}{9 \times 3} = \frac{28}{27} = 1\frac{1}{27}$$
Ответ: $$1\frac{1}{27}$$