\(\frac{48}{54}-x=\frac{7}{8}\Rightarrow\frac{8}{9}-x=\frac{7}{8}\)
\(\Rightarrow x=\frac{8}{9}-\frac{7}{8}=\frac{8\cdot8-9\cdot7}{72}=\frac{1}{72}\)
Vậy \(x=\frac{1}{72}\)
\(\frac{55}{60}-x=\frac{30}{45}\Rightarrow\frac{11}{12}-x=\frac{2}{3}\)
\(\Rightarrow\frac{11}{12}-\frac{12x}{12}=\frac{8}{12}\)
\(\Rightarrow11-12x=8\)
\(\Rightarrow12x=3\)
\(\Rightarrow4x=1\Rightarrow x=\frac{1}{4}\)
Vậy \(x=\frac{1}{4}\)