Cách làm cho bạn:
a) $\frac{x}{4}$ = $\frac{16}{128}$ $\Rightarrow$ $\frac{x}{4}$ = $\frac{1}{8}$ $\Rightarrow$ x.8 = 4.1 $\Rightarrow$ x = $\frac{1}{2}$;
b)1$\frac{5}{6}$ = $\frac{-x}{5}$ $\Rightarrow$ $\frac{11}{6}$ = $\frac{-x}{5}$ $\Rightarrow$ 6.(-x) = 11.5 $\Rightarrow$ x = $\frac{-55}{6}$;
c) 4,25:8 = -3,5:x $\Rightarrow$ x = $\frac{-3,5}{4,25:8}$ $\Rightarrow$ x = $\frac{-112}{17}$.
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