a: \(12:\dfrac{3}{4}+75\%\cdot\dfrac{1}{2}-16\cdot50\%\)

\(=12\cdot\dfrac{4}{3}+\dfrac{3}{4}\cdot\dfrac{1}{2}-16\cdot0,5\)

\(=16-8+\dfrac{3}{8}\)

\(=8,375\)

b: \(75\%\cdot4+22,5:3-1\dfrac{3}{5}\)

\(=0,75\cdot4+7,5-1,6\)

\(=3+7,5-1,6\)

=10,5-1,6

=8,9

a) \(\frac{1}{2}x+\frac{3}{5}\left(x-2\right)=3\)

 0,5 x + 0,6 ( x - 2 ) = 3

0,5 x + 0.6 x - 1,2 = 3

1,1 x = 4,2

x = \(\frac{42}{11}\)

Kết luận: 

b) \(\frac{1}{3}x-0,5x=0,75\)

\(\frac{1}{3}x-\frac{1}{2}x=\frac{3}{4}\)

\(-\frac{1}{6}x=\frac{3}{4}\)

\(x=-\frac{9}{2}\)

Kết luận: 

c) \(\frac{3}{-2}x-0,5x=75\%\)

-1,5x - 0,5x = 0,75 

-2x = 0,75 

x = -0,375

Kết luận: 

d) \(-\frac{2}{5}x+\frac{1}{4}=75\%-\frac{3}{4}x\)

-0,4 x + 0,25 = 0,75 - 0,75 x 

-0,4 x + 0,75 x = 0,75 - 0,25

0,35 x = 0,5 

x = \(\frac{10}{7}\)

Kết luận: 

\(a,\frac{1}{2}x+\frac{3}{5}\left(x-2\right)=3\)

\(\frac{1}{2}x+\frac{3}{5}x-\frac{6}{5}=3\)

\(\left(\frac{1}{2}+\frac{3}{5}\right)x-\frac{6}{5}=3\)

\(\frac{11}{10}x-\frac{6}{5}=3\)

\(\frac{11}{10}x=\frac{21}{5}\)

\(x=\frac{42}{11}\)

\(b,\frac{1}{3}x-\frac{1}{2}x=\frac{3}{4}\)

\(\left(\frac{1}{3}-\frac{1}{2}\right)x=\frac{3}{4}\)

\(\frac{-1}{6}x=\frac{3}{4}\)

\(x=\frac{-9}{2}\)

\(c,\frac{3}{-2}x-\frac{1}{2}x=75\%\)

\(\left(\frac{3}{-2}-\frac{1}{2}\right)x=\frac{3}{4}\)

\(-2x=\frac{3}{4}\)

\(x=\frac{-3}{8}\)

\(\frac{-2}{5}x+\frac{1}{4}=75\%-\frac{3}{4}x\)

\(\frac{-2}{5}x+\frac{3}{4}x=\frac{3}{4}-\frac{1}{4}\)

\(\left(\frac{-2}{5}+\frac{3}{4}\right)x=\frac{1}{2}\)

\(\frac{7}{20}x=\frac{1}{2}\)

\(x=\frac{10}{7}\)

\(\frac{1}{3}.x+\frac{3}{4}.x-75\%=\frac{-51}{4}\)

\(x.\left(\frac{1}{3}+\frac{3}{4}\right)-\frac{3}{4}=\frac{-51}{4}\)

\(x.\left(\frac{4}{12}+\frac{9}{12}\right)=\frac{-51}{4}+\frac{-3}{4}\)

\(x.\frac{13}{12}=\frac{-54}{4}=\frac{-27}{2}\)

\(x=\frac{-27}{2}:\frac{13}{12}=\frac{-27}{2}.\frac{2}{13}=\frac{-27.2}{2.13}=\frac{-27.1}{1.13}=\frac{-27}{13}\)

Xin lỗi cho mình sửa lại

\(\frac{1}{3}.x+\frac{3}{4}.x-75\%=\frac{-51}{4}\)

\(x.\left(\frac{1}{3}+\frac{3}{4}\right)-\frac{3}{4}=\frac{-51}{4}\)

\(x.\left(\frac{4}{12}+\frac{9}{12}\right)=\frac{-51}{4}+\frac{3}{4}=\frac{-48}{4}\)

\(x.\frac{13}{12}=-12\)

\(x=-12:\frac{13}{12}=12.\frac{12}{13}=\frac{-12.12}{13}=\frac{-144}{13}\)

\(a,x.\frac{3}{4}-1=\frac{2}{75}\)

\(x.\frac{3}{4}=\frac{77}{75}\)

\(x=\frac{77}{75}:\frac{3}{4}=\frac{308}{225}\)

\(b,3-x:\frac{2}{3}=75\)

\(x:\frac{2}{3}=-72\)

\(x=-72.\frac{2}{3}=-48\)

\(\frac{1}{3}.x+\frac{3}{4}.x-75\%=-\frac{21}{4}\)

      \(\frac{1}{3}.x+\frac{3}{4}.x-\frac{3}{4}=-\frac{21}{4}\)

               \(x.\left(\frac{1}{3}+\frac{3}{4}\right)=-\frac{21}{4}+\frac{3}{4}\)

                              \(x.\frac{13}{12}=-\frac{9}{2}\)

                                       \(x=-\frac{9}{2}:\frac{13}{12}\)

                                        \(x=-\frac{54}{13}\)

=> x.(1/3+3/4) -75/100=-21/4

=> x .13/12   -  3/4     =21/4

=> x. 13/12                =21/4 + 3/4

=> x.13/12                 =6

=> x                          = 6 : 13/12

=> x                          = 72/13

vậy x= 72/13

       1/3 x X + 3/4 x X - 75% = -21/4

<=> 13/12 x X = -21/4 + 75/100

<=> 13/12 x X = -525/100 + 75/100

<=> 13/12 x X = -9/2

<=> X = -54/13

\(75\%x-x=1-\frac{3}{4}\)

\(\Rightarrow\frac{75}{100}.x-x=\frac{1}{4}\)

\(\Rightarrow\frac{3}{4}x-x=\frac{1}{4}\)

\(\Rightarrow x.\left(\frac{3}{4}-1\right)=\frac{1}{4}\)

\(\Rightarrow x.\frac{-1}{4}=\frac{1}{4}\)

\(\Rightarrow x=-1\)