286 a) \frac{3}{12}, \frac{5}{15}, \frac{4}{20}, \frac{5}{50}, \frac{9}{18}, \frac{10}{40}

Сократим дроби:

• $$\frac{3}{12} = \frac{3 \cdot 1}{3 \cdot 4} = \frac{1}{4}$$
• $$\frac{5}{15} = \frac{5 \cdot 1}{5 \cdot 3} = \frac{1}{3}$$
• $$\frac{4}{20} = \frac{4 \cdot 1}{4 \cdot 5} = \frac{1}{5}$$
• $$\frac{5}{50} = \frac{5 \cdot 1}{5 \cdot 10} = \frac{1}{10}$$
• $$\frac{9}{18} = \frac{9 \cdot 1}{9 \cdot 2} = \frac{1}{2}$$
• $$\frac{10}{40} = \frac{10 \cdot 1}{10 \cdot 4} = \frac{1}{4}$$

Ответ: $$\frac{1}{4}$$, $$\frac{1}{3}$$, $$\frac{1}{5}$$, $$\frac{1}{10}$$, $$\frac{1}{2}$$, $$\frac{1}{4}$$