40%.x+55%.x=20%
<=>\(\frac{2}{5}.x+\frac{11}{20}.x=\frac{1}{5}\)
<=>\(x\left(\frac{2}{5}+\frac{11}{20}\right)=\frac{1}{5}\)
<=>\(x\frac{19}{20}=\frac{1}{5}\)
<=>\(x=\frac{4}{19}\)
Vậy \(x=\frac{4}{19}\)
40%.x+55%.x=20%
x.(40%+55%)=20%
x.95% =20%
x =20% - 95%
x =-3/4