3. Найдите произведение или частное: 1) a) $$\frac{7}{16} \cdot \frac{8}{21}$$; 2) a) $$3\frac{1}{4} \cdot 3\frac{9}{13}$$; 3) a) $$\frac{5}{7} : (-\frac{10}{21})$$; 4) a) $$\frac{5}{9} \cdot (-9)$$; 5) a) $$6,5 \cdot 2,6$$ 6) a) $$0,81:0,009$$

1) a) $$\frac{7}{16} \cdot \frac{8}{21} = \frac{7 \cdot 8}{16 \cdot 21} = \frac{1 \cdot 1}{2 \cdot 3} = \frac{1}{6}$$ 2) a) $$3\frac{1}{4} \cdot 3\frac{9}{13} = \frac{13}{4} \cdot \frac{48}{13} = \frac{13 \cdot 48}{4 \cdot 13} = \frac{1 \cdot 12}{1 \cdot 1} = 12$$ 3) a) $$\frac{5}{7} : (-\frac{10}{21}) = \frac{5}{7} \cdot (-\frac{21}{10}) = -\frac{5 \cdot 21}{7 \cdot 10} = -\frac{1 \cdot 3}{1 \cdot 2} = -\frac{3}{2} = -1\frac{1}{2}$$ 4) a) $$\frac{5}{9} \cdot (-9) = -\frac{5 \cdot 9}{9} = -5$$ 5) a) $$6,5 \cdot 2,6 = 16,9$$ 6) a) $$0,81:0,009 = 810:9 = 90$$