4. Найди неизвестный член пропорции: a) 3,2: 2,8 = y : 2,1; b) \frac{z}{4} = \frac{105}{70}; c) y:\frac{6}{7} = 1\frac{1}{6}:3\frac{1}{2};

a) 3,2 : 2,8 = y : 2,1

$$y = \frac{3,2 \cdot 2,1}{2,8} = \frac{3,2 \cdot 21}{28} = \frac{3,2 \cdot 3}{4} = 0,8 \cdot 3 = 2,4$$

b) $$\frac{z}{4} = \frac{105}{70}$$

$$z = \frac{4 \cdot 105}{70} = \frac{4 \cdot 15}{10} = \frac{2 \cdot 15}{5} = 2 \cdot 3 = 6$$

c) $$y:\frac{6}{7} = 1\frac{1}{6}:3\frac{1}{2}$$

$$y:\frac{6}{7} = \frac{7}{6}:\frac{7}{2}$$

$$y:\frac{6}{7} = \frac{7}{6} \cdot \frac{2}{7}$$

$$y:\frac{6}{7} = \frac{1}{3}$$

$$y = \frac{6}{7} \cdot \frac{1}{3} = \frac{2}{7}$$

Ответ: a) y = 2,4; b) z = 6; c) y = $$\frac{2}{7}$$