ko đc đâu bn:)

:))) mik bt mà , quá 3p r , mik ko sửa đc nx 

\(\dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)-2=20\%\\ \dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)-2=\dfrac{1}{5}\\ \dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)=\dfrac{1}{5}+2\\ \dfrac{2}{5}\left(1-\dfrac{1}{2}x\right)=\dfrac{11}{5}\\ 1-\dfrac{1}{2}x=\dfrac{11}{5}\cdot\dfrac{5}{2}\\ 1-\dfrac{1}{2}x=\dfrac{11}{2}\\ \dfrac{1}{2}x=-\dfrac{9}{2}\\ x=-\dfrac{9}{2}\cdot2=x=-9\)

\(a,25\times432\times4=25\times4\times432=100\times432=4320\\ b,456\times200-456\times100=456\times\left(200-100\right)=456\times100=45600\)