x + ( x + 10 ) + ( x + 20) + (x+ 30 ) + ... + ( x + 100 ) = 770

( x + x + x +... x) + ( 10 + 20 + 30 + ...... + 100) = 770

      X x 11    + 550 = 770

        X x 11 = 770 - 550

           X x 11 = 220 

              x      = 220 : 11

              x = 20

10(x-2)-8x+20=x-30

<=>10x-20-8x+20=x-30

<=>2x                  =x-30

<=>2x-x              =-30

  <=>     x             =-30

Vậy x =-30

Chúc bạn học tốt, nhớ mk nha

10(x-2)-8x+20=x-30

10x-20-8x+20=x-30

10x-8x-x        =-30+20-20

x                    =-30

 Vậy x=-30

       10(x-2)-8x+20=x-30

<=> 10x-20-8x+20=x-30

<=> 10x-8x-x        = -30+20-20

<=> x                    =-30

 Vậy X= -30

\(-\left(\frac{3}{10}-\frac{6}{11}\right)-\left(\frac{21}{30}-\frac{5}{11}\right)-\left(-\frac{1}{2}+20\%\right)\)

\(=-\frac{3}{10}+\frac{6}{11}-\frac{21}{30}+\frac{5}{11}+\frac{1}{2}+\frac{20}{100}\)

\(=-\frac{3}{10}-\frac{7}{10}+\frac{6}{11}+\frac{5}{11}+\frac{1}{2}+\frac{1}{5}\)

\(=-1+1+\frac{7}{10}\)

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

\(\dfrac{21}{36}-\left(-\dfrac{11}{30}\right)=\dfrac{7}{12}+\dfrac{11}{30}=\dfrac{7.5+11.2}{60}=\dfrac{57}{60}=\dfrac{19}{20}\\ ----\\\dfrac{-4}{8}+\left(-\dfrac{3}{10}\right)=\dfrac{-1}{2}-\dfrac{3}{10}=\dfrac{-1.5-3}{10}=\dfrac{-8}{10}=-\dfrac{4}{5}\\ ----\\ \dfrac{7}{12}-\left(-\dfrac{9}{20}\right)=\dfrac{7}{12}+\dfrac{9}{20}=\dfrac{7.5+9.3}{60}=\dfrac{62}{60}=\dfrac{31}{30}\\ ---\\ \dfrac{-2}{5}+\left(-\dfrac{11}{30}\right)=-\dfrac{2}{5}-\dfrac{11}{30}=\dfrac{-2.6-11}{30}=-\dfrac{29}{30}\)

\(30-x:4X5=20\)

      \(30-x:4=20:5\)

      \(30-x:4=4\)

          \(30-x=4X4\)

          \(30-x=16\)

                      \(x=30-16\)

                      \(x=14\)

ta có: 30-x : 4=20:5=4

         30-X=4*4=16

         X=30-16=14

vậy x=14

k cho mình nha

20

30

40

60

60

90

10+10=20

10+10+10=30

20+20=40

20+20+20=60

30+30=60

30+30+30=90

tk mình nhé

10 + 10 = 20

10+10+10=30

20+20=40

20+20+20=60

30+30=60

30+30+30=90