3. Вычислите: a) $$\frac{4}{9}\cdot(-\frac{3}{8})$$ b) $$\frac{5}{6}-\frac{4}{9}+\frac{16}{21}$$

a) $$\frac{4}{9}\cdot(-\frac{3}{8})=-\frac{4\cdot3}{9\cdot8}=-\frac{12}{72}=-\frac{1}{6}$$

Ответ: $$-\frac{1}{6}$$

б) $$\frac{5}{6}-\frac{4}{9}+\frac{16}{21}=\frac{5\cdot63-4\cdot42+16\cdot18}{378}=\frac{315-168+288}{378}=\frac{435}{378}=\frac{145}{126}$$

Ответ: $$\frac{145}{126}$$