3. а) $$ \frac{5}{9} = \frac{5 \cdot 2}{9 \cdot 2} = \frac{10}{18}, \frac{5}{9} = \frac{5 \cdot 5}{9 \cdot 5} = \frac{25}{45}, \frac{5}{9} = \frac{5 \cdot 20}{9 \cdot 20} = \frac{100}{180}$$.
б) $$ \frac{16}{24} = \frac{8 \cdot 2}{8 \cdot 3} = \frac{2}{3}, \frac{18}{30} = \frac{6 \cdot 3}{6 \cdot 5} = \frac{3}{5}, \frac{60}{160} = \frac{20 \cdot 3}{20 \cdot 8} = \frac{3}{8}$$.
Ответ: а) $$ \frac{10}{18}, \frac{25}{45}, \frac{100}{180}$$; б) $$ \frac{2}{3}, \frac{3}{5}, \frac{3}{8}$$