4. Найди неизвестный член пропорции: a) y: 6,8 = 1,3: 3,4 102 z b) = 34 28', 1 3 3 c) 1-:y=4-:2-. 2 4 8

a) y : 6,8 = 1,3 : 3,4

$$y = \frac{6.8 \cdot 1.3}{3.4} = \frac{6.8}{3.4} \cdot 1.3 = 2 \cdot 1.3 = 2.6$$

b) $$\frac{102}{34} = \frac{z}{28}$$

$$z = \frac{102 \cdot 28}{34} = 3 \cdot 28 = 84$$

c) $$1\frac{1}{2} : y = 4\frac{3}{4} : 2\frac{3}{8}$$

$$\frac{3}{2} : y = \frac{19}{4} : \frac{19}{8}$$

$$y = \frac{\frac{3}{2} \cdot \frac{19}{8}}{\frac{19}{4}} = \frac{3}{2} \cdot \frac{19}{8} \cdot \frac{4}{19} = \frac{3 \cdot 4}{2 \cdot 8} = \frac{3}{4} = 0.75$$

Ответ: а) y = 2.6; b) z = 84; c) y = 0.75