1)х 8-ых = 2 7-ых 3)3 х(в дроби) = 7 15-ых

Решите задачу:

$\frac{x}{8} =\frac{2}{7}\quad \Rightarrow \quad x= \frac{2\cdot 8}{7}= \frac{16}{7}=2 \frac{2}{7}\\\\ \frac{3}{x}=\frac{7}{15}\quad \Rightarrow \quad x=\frac{3\cdot 15}{7}=\frac{45}{7}=6 \frac{3}{7}\\\\\\P.S.\; \; \; \; \frac{x}{a}=\frac{b}{c}\quad \Rightarrow \quad x= \frac{a\cdoy b}{c}\; ;\\\\ \frac{a}{x}=\frac{b}{c}\quad \Rightarrow \quad x=\frac{a\cdot c}{b} \; .$