Đáp án là B

\(\frac{X}{2}=\frac{Y}{3}=\frac{Z}{4}\)\(=\frac{X}{2}=\frac{2Y}{6}=\frac{3Z}{12}\)\(=\frac{X+2Y-3Z}{2+6-12}\)\(=5\)

\(=>X=2.5=10\)

\(=>y=3.5=15\)

\(=>z=4.5=20\)

vậy.....

1 ) ( x - 15 ) : 2 = 10

x - 15 = 10 x 2

x - 15 = 20

x = 20 + 15

x = 35

2 ) 19 - 9 . ( x - 10 ) = 1

9 . ( x - 10 ) = 19 - 1

9 . ( x - 10 ) = 18

x - 10 = 18 : 9

x - 10 = 2

x = 10 + 2 

x = 12

21 . x + 21 . 10 = 2100

21 . ( x + 10 ) = 2100

x + 10 = 2100 : 21

x + 10 = 100

x = 100 - 10

x = 90

( x - 15 ) :2 = 10

 x - 15     = 10 : 2

x - 15        = 5

x               = 5 + 15

x                20

19 - 9 * ( x - 10 ) = 1

       9 * ( x - 10 ) = 19 -1

       9 *  ( x - 10 ) = 18

                x - 10= 18:9

                 x - 10 = 2

                 x         = 2 +10

                x          = 12

21 * x + 21 * 10 = 2100

21 * ( x + 10 )     = 2100

          x + 10      = 2100 : 21

          x + 10      =100

           x             = 100 - 10

            x             = 90

Cần đáp án thoi

A

\(x\) + \(\dfrac{1}{10}\) + \(x\) + \(\dfrac{1}{10}\) = \(x\) + \(\dfrac{1}{21}\)

\(x+x\) - \(x\)  =  \(\dfrac{1}{21}\) -  \(\dfrac{1}{10}\) - \(\dfrac{1}{10}\) 

         \(x\)    = \(\dfrac{1}{21}\)  - \(\dfrac{1}{5}\) 

          \(x\) = - \(\dfrac{16}{105}\) 

a) \(\dfrac{24}{25}-x=\dfrac{3}{5}\)

\(x=\dfrac{24}{25}-\dfrac{3}{5}\)

\(x=\dfrac{24}{25}-\dfrac{15}{25}\)

\(x=\dfrac{9}{25}\)

b) \(\dfrac{4}{7}-\dfrac{x}{21}=\dfrac{10}{21}\)

\(\dfrac{x}{21}=\dfrac{4}{7}-\dfrac{10}{21}\)

\(\dfrac{x}{21}=\dfrac{12}{21}-\dfrac{10}{21}\)

\(\dfrac{x}{21}=\dfrac{2}{21}\)

\(x=2\)

a) 24/25 - x = 3/5

                 x =24/25 - 3/5

                 x = 24/25 - 15/25

                 x = 9/15 

                 x = 3/5

Vậy x = 3/5

b)4/7 - x/21 = 10/21

            x/21 = 4/7 - 10/21

            x/21 = 12/21 - 10/21

            x/21 = 2/21

vậy x = 2

----------------nếu thấy đúng thì cho mình xin 1like nhó-------------------------

\(121-5.\left(60-5x\right)=21^{10}:\left(21^6.21^3\right)\)

\(121-5.\left(60-5x\right)=21^{10}:21^9\)

\(121-5.\left(60-5x\right)=21\)

\(5.\left(60-5x\right)=121-21\)

\(5.\left(60-5x\right)=100\)

\(60-5x=100:5\)

\(60-5x=20\)

\(5x=60-20\)

\(5x=20\)

\(\Rightarrow x=4\)

\(121-5.\left(60-5x\right)=21^{10}:\left(21^6.21^3\right)\)

\(121-300+25x=21^{10}:21^{11}\)

\(25x-179=\frac{1}{21}\)

\(25x=\frac{1}{21}+179\)

\(25x=\frac{3760}{21}\)

\(x=\frac{3760}{21}:25\)

\(x=\frac{752}{105}\)

vay \(x=\frac{752}{105}\)

\(\left(x+1\right)\left(21-1\right)=-21\)

\(\left(x+1\right)\cdot20=-21\)

\(x+1=\frac{-21}{20}\)

\(x=\frac{-21}{20}-1\)

\(x=\frac{-41}{20}\)

( x + 1 ) . ( 21 - 1 ) = -21

( x + 1 ) . 20          = -21

( x + 1 )               =   -21 : 20

( x + 1 )                =  1.05

x                          =   1,05 - 1

x                         =   - 0 ,05

x ( 2x + 3 ) = 10

Xét bảng :

Vậy ko có giá trị của x thỏa mãn

\(\dfrac{x-2023}{6}+\dfrac{x-2023}{10}+\dfrac{x-2023}{15}+\dfrac{x-2023}{21}=\dfrac{8}{21}\)

\(\left(x-2023\right)\left(\dfrac{1}{6}+\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}\right)=\dfrac{8}{21}\)

\(\left(x-2023\right).\dfrac{8}{21}=\dfrac{8}{21}\)

\(x-2023=1\)

\(x=2024\)

Vậy..............

\(...\Rightarrow\left(x-2023\right)\left(\dfrac{1}{6}+\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}\right)=\dfrac{8}{21}\)

\(\Rightarrow\left(x-2023\right)\left(\dfrac{35+21+14+1}{210}\right)=\dfrac{8}{21}\)

\(\Rightarrow\left(x-2023\right).\dfrac{71}{210}=\dfrac{8}{21}\)

\(\Rightarrow\left(x-2023\right).\dfrac{71}{210}=\dfrac{8}{21}.\dfrac{210}{71}=\dfrac{80}{71}\)

\(\Rightarrow x-2023=\dfrac{80}{71}\Rightarrow x=\dfrac{80}{71}+2023=\dfrac{143713}{71}\)

\(\dfrac{x-2023}{6}+\dfrac{x-2023}{10}+\dfrac{x-2023}{15}+\dfrac{x-2023}{21}=\dfrac{8}{21}\)

\(\Leftrightarrow\left(x-2023\right).\left(\dfrac{1}{6}+\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}\right)=\dfrac{8}{21}\)

\(\Leftrightarrow\left(x-2023\right).\left(\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}\right)=\dfrac{4}{21}\)

\(\Leftrightarrow\left(x-2023\right).\left(\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}\right)=\dfrac{4}{21}\)

\(\Leftrightarrow\left(x-2023\right).\left(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}\right)=\dfrac{4}{21}\)

\(\Leftrightarrow\left(x-2023\right).\left(\dfrac{1}{3}-\dfrac{1}{7}\right)=\dfrac{4}{21}\)

\(\Leftrightarrow x-2023=1\Leftrightarrow x=2024\)