2) Вычислите: a) $$\frac{7}{9} + \frac{1}{9}$$; б) $$\frac{6}{15} - \frac{1}{15}$$; в) $$\frac{17}{23} - \frac{6}{23} + 1$$; г) $$\frac{1}{2} - \frac{1}{8}$$; д) $$\frac{9}{12} - \frac{5}{12}$$; ж) $$\frac{4}{7} \cdot \frac{14}{8}$$; з) $$\frac{3}{5} : \frac{3}{4}$$; и) $$\frac{4}{17} : \frac{3}{17} : \frac{3}{4}$$

a) $$\frac{7}{9} + \frac{1}{9} = \frac{7+1}{9} = \frac{8}{9}$$

б) $$\frac{6}{15} - \frac{1}{15} = \frac{6-1}{15} = \frac{5}{15} = \frac{1}{3}$$

в) $$\frac{17}{23} - \frac{6}{23} + 1 = \frac{17-6}{23} + 1 = \frac{11}{23} + 1 = \frac{11}{23} + \frac{23}{23} = \frac{11+23}{23} = \frac{34}{23} = 1 \frac{11}{23}$$

г) $$\frac{1}{2} - \frac{1}{8} = \frac{4}{8} - \frac{1}{8} = \frac{4-1}{8} = \frac{3}{8}$$

д) $$\frac{9}{12} - \frac{5}{12} = \frac{9-5}{12} = \frac{4}{12} = \frac{1}{3}$$

ж) $$\frac{4}{7} \cdot \frac{14}{8} = \frac{4 \cdot 14}{7 \cdot 8} = \frac{4 \cdot 2 \cdot 7}{7 \cdot 4 \cdot 2} = 1$$

з) $$\frac{3}{5} : \frac{3}{4} = \frac{3}{5} \cdot \frac{4}{3} = \frac{3 \cdot 4}{5 \cdot 3} = \frac{4}{5}$$

и) $$\frac{4}{17} : \frac{3}{17} : \frac{3}{4} = \frac{4}{17} \cdot \frac{17}{3} \cdot \frac{4}{3} = \frac{4 \cdot 17 \cdot 4}{17 \cdot 3 \cdot 3} = \frac{16}{9} = 1 \frac{7}{9}$$