а) 2$$\frac{1}{7}$$\cdot 3$$\frac{1}{9}$$ = $$\frac{15}{7}$$\cdot$$\frac{28}{9}$$ = $$\frac{15 \cdot 28}{7 \cdot 9}$$ = $$\frac{15 \cdot 4}{1 \cdot 9}$$ = $$\frac{60}{9}$$ = 6$$\frac{6}{9}$$ = 6$$\frac{2}{3}$$
б) $$\frac{3}{7}$$\cdot$$\frac{7}{9}$$ = $$\frac{3 \cdot 7}{7 \cdot 9}$$ = $$\frac{1 \cdot 1}{1 \cdot 3}$$ = $$\frac{1}{3}$$
в) $$\frac{5}{8}$$\cdot 1$$\frac{13}{15}$$\cdot 2$$\frac{2}{7}$$ = $$\frac{5}{8}$$\cdot$$\frac{28}{15}$$\cdot$$\frac{16}{7}$$ = $$\frac{5 \cdot 28 \cdot 16}{8 \cdot 15 \cdot 7}$$ = $$\frac{1 \cdot 4 \cdot 2}{1 \cdot 3 \cdot 1}$$ = $$\frac{8}{3}$$ = 2$$\frac{2}{3}$$
Ответ: а) 6$$\frac{2}{3}$$; б) $$\frac{1}{3}$$; в) 2$$\frac{2}{3}$$