X = 47,250

Chọn C

C

\(1.x-\dfrac{2}{3}\times\left(x+9\right)=1\)

\(x-\dfrac{2}{3}\times x-6=1\)

\(x\times\left(1-\dfrac{2}{3}\right)=7\)

\(x\times\dfrac{1}{3}=7\)

\(x=21\)

\(2.x-\dfrac{11}{15}=\dfrac{3+x}{5}\)

\(\dfrac{15x}{15}-\dfrac{11}{15}=\dfrac{9+3x}{15}\)

\(15x-11=9+3x\)

\(12x=20\)

\(x=\dfrac{5}{3}\)

\(\left(x\times1\right)+\left(x\times2\right)+...+\left(x\times9\right)=405\)

\(\Rightarrow x\left(1+2+3+...+9\right)=405\)

\(\Rightarrow x\times45=405\)

\(\Rightarrow x=405:45\)

\(\Rightarrow x=9\)

Xyz sao mình tính được là 405:50 là có dư

Để mình viết đề lại cho nhé:

\(x\times14-x:\frac{1}{9}+\frac{1}{9}=\frac{3}{11}\)

\(x\times14-x\times9+\frac{1}{9}=\frac{3}{11}\)

\(x\times\left(14-9\right)=\frac{3}{11}-\frac{1}{9}\)

\(x\times5=\frac{27}{99}-\frac{11}{99}\)

\(x\times5=\frac{16}{99}\)

\(x=\frac{16}{99}:5\)

\(x=\frac{16}{495}\)

x * 14 - x : 1/9 + 1/9 = 3/11

x * 14 - x * 9 + 1/9    = 3/11

x * (14 - 9) + 1/9       = 3/11

x * 5 + 1/9               = 3/11

x * 5                        = 3/11 - 1/9

x * 5                        = 16/99

x                             = 16/99 : 5

x                             = 16/495

X+X*9=9990

X+X   =9990/9

X+X   =1110

        X =1110/2

        X  =555

X+X=9990/9

X+X=1110

X*2=1110

X=1110/2

X=555

\(342< 9\times X< 360\)

\(342:9< X< 360:9\)

\(38< X< 40\)

\(X=39\)

x + 1 + x + 3 +x + 5 + x + 7 + x + 9 = 750

  ( x + x + x + x + x ) + ( 1 + 3 + 5 + + 7 + 9 ) = 750

     x x 5 + 25 = 750

     x x 5 = 750 - 25

     x x  5 = 725

           x = 725 :5

           x = 145

x=750:(1+3+5+7+9)

x=750:25

x=30

a)4/9 : x/6 = 2/3

           x/6 = 4/9 : 2/3

          x/6  =   2/3 = 4/6

vậy x = 4

b)x/5 x 3/7 = 9/35

   x/5          = 9/35 : 3/7

   x/5          = 3/5

vậy x = 3