3. Решите уравнение: 1) 6:5=x: 75; 3) \frac{x}{0,8}=\frac{15}{4}; 2) a:1\frac{7}{50}=\frac{5}{57}:2\frac{1}{2}; 4) \frac{5-y}{4}=\frac{3}{7}.

Решение уравнений:

1. $$6:5 = x:75$$

   $$\frac{6}{5} = \frac{x}{75}$$

   $$x = \frac{6 \cdot 75}{5} = \frac{450}{5} = 90$$

   Ответ: 90

2. $$a:1\frac{7}{50}=\frac{5}{57}:2\frac{1}{2}$$

   $$a:\frac{57}{50} = \frac{5}{57}:\frac{5}{2}$$

   $$a:\frac{57}{50} = \frac{5}{57} \cdot \frac{2}{5}$$

   $$a:\frac{57}{50} = \frac{2}{57}$$

   $$a = \frac{2}{57} \cdot \frac{57}{50}$$

   $$a = \frac{1}{25}$$

   Ответ: 1/25

3. $$\frac{x}{0,8} = \frac{15}{4}$$

   $$x = \frac{15 \cdot 0,8}{4} = \frac{12}{4} = 3$$

   Ответ: 3

4. $$\frac{5-y}{4} = \frac{3}{7}$$

   $$5-y = \frac{3 \cdot 4}{7}$$

   $$5-y = \frac{12}{7}$$

   $$y = 5 - \frac{12}{7}$$

   $$y = \frac{35}{7} - \frac{12}{7} = \frac{23}{7} = 3\frac{2}{7}$$

   Ответ: 23/7