x - 20% * x = 216
x*( 1-20%)=216
x* ( 1-\(\frac{1}{5}\))=216
x*( \(\frac{5}{5}\)-\(\frac{1}{5}\))=216
x*\(\frac{4}{5}\)=216
x=216 : \(\frac{4}{5}\)
x = 216* \(\frac{5}{4}\)
x = 270
x-20%*x=216
x*(1-20%)=216
x*4/5=216
x=216:4/5
x=270
Vậy x=270
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