Найдите неизвестный член пропорции: a) x : 12 = 5 : 4 в) 2,5 : 4 = x : 8 б) 18 : x = 6 : 7 г) 9,2 : 2 = 27 : x

Найдем неизвестный член пропорции:

1. a) $$ x : 12 = 5 : 4 $$, $$ \frac{x}{12} = \frac{5}{4} $$, $$ x = \frac{12 \cdot 5}{4} = \frac{60}{4} = 15 $$.
2. в) $$ 2.5 : 4 = x : 8 $$, $$ \frac{2.5}{4} = \frac{x}{8} $$, $$ x = \frac{2.5 \cdot 8}{4} = \frac{20}{4} = 5 $$.
3. б) $$ 18 : x = 6 : 7 $$, $$ \frac{18}{x} = \frac{6}{7} $$, $$ x = \frac{18 \cdot 7}{6} = \frac{126}{6} = 21 $$.
4. г) $$ 9.2 : 2 = 27 : x $$, $$ \frac{9.2}{2} = \frac{27}{x} $$, $$ x = \frac{27 \cdot 2}{9.2} = \frac{54}{9.2} = \frac{540}{92} = \frac{135}{23} \approx 5.87 $$.

Ответ: a) x = 15, в) x = 5, б) x = 21, г) x = 135/23 ≈ 5.87