bn l-ike cho mk trước đã

Ta có : A=20/11×13 + 20/13×15 +20/15×17+...+20/53×55

A = 10 ×( 2/11×13+2/13×15+...12/53×55)

A = 10 ×(1/11-1/13+1/13-1/15+1/15-1/17+...+1/53-1/55)

A = 10 × (1/11-1/55)

A =10 × 4/55

A = 8/11

X + 0,2 x X = 7,2

1,2 x X = 7,2

X = 7,2 : 1,2

X = 6

Đúng 100%

Đúng 100%

Đúng 100%

Ta có: \(x+20\%x=7,2\)

<=>\(x+0,2x=7,2\)

<=>\(x\left(1+0,2\right)=7,2\)

<=>\(1,2x=7,2\)

<=>\(x=7,2:1,2\)

<=>\(x=6\)

Vậy:\(x=6\)

\(\frac{x-2}{12}+\frac{x-2}{20}+\frac{x-2}{30}+..+\frac{x-2}{72}=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{72}\right)=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{8.9}\right)=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{8}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Rightarrow\left(x-2\right).\left(\frac{1}{3}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Rightarrow x-2=0\Rightarrow x=2\)

sai rồi nha hoàng trung kiên

Ta có : 

\(\frac{x-2}{12}+\frac{x-2}{20}+\frac{x-2}{30}+\frac{x-2}{42}+\frac{x-2}{56}+\frac{x-2}{72}=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right)\left(\frac{1}{3}-\frac{1}{9}\right)=\frac{16}{9}\)

\(\Leftrightarrow\)\(\left(x-2\right).\frac{2}{9}=\frac{16}{9}\)

\(\Leftrightarrow\)\(x-2=\frac{16}{9}:\frac{2}{9}\)

\(\Leftrightarrow\)\(x-2=\frac{16}{9}.\frac{9}{2}\)

\(\Leftrightarrow\)\(x-2=\frac{8}{1}.\frac{1}{1}\)

\(\Leftrightarrow\)\(x-2=8\)

\(\Leftrightarrow\)\(x=8+2\)

\(\Leftrightarrow\)\(x=10\)

Vậy \(x=10\)

Chúc bạn học tốt ~ 

x(100%+20%)=7.2

x120%=720%

x=720%:120%

x=6

vậy////////

(40%+100%)x+20%=720%

140%x=720%-20%

140%x=700%

x=720%:140%

x=36/7

vậy x=/////////////

x﴾100%+20%﴿

=7.2 x120%

=720% x

=720%:120%

x=6 

\(40\%\times x+x\times20\%=72\)

\(\left(40\%+20\%\right)\times x=72\)

                     \(60\%\times x=72\)

                                    \(x=72:60\%\)

                                    \(x=120\)

b) 54,3 x 4,7 + 54,3 x 4,3 + 54,3

= 54,3 x (4,7 + 4,3 + 1)

= 54,3 x 10

= 543

\(X\times20o/o+X=7,2\)

\(\Leftrightarrow\)2x+0,2=7,2

\(\Leftrightarrow\)2x     =7,2-0,2

\(\Leftrightarrow\)2x     = 7

\(\Rightarrow\) x        =7:2

\(\Rightarrow\)x        =3,5

\(40o/o\times X+X\times20o/o=72\)

\(\Leftrightarrow0,4\times X+X\times0,2=72\)

\(\Leftrightarrow X\times\left(0,4+0,2\right)=72\)

\(\Leftrightarrow X\times0,6=72\)

\(\Rightarrow X=72:0,6\)

\(\Rightarrow X=120\)

40%*x+x*20%=72

-> 0,4x+ 0,2 x= 72

-> 0,6 x= 72

-> x=120

a) 12-3x=0

    3x=12-0

    3x=12

    x=12:3

    x=4

b)2x-26=25.12

   2x-26=300

   2x=300+26

   2x=326

   x=326:2

   x=163

c)5x+28=234:3

  5x+28=78

  5x=78-28

  5x=50

  x=50:5

  x=10

d)72-7x=529:23

   72-7x=23

   7x=72-23

   7x=49

   x=49:7

   x=7

k cho mình nhoa~~

a, (12-3x):20=0

=> 12-3x=0

=> 3x=12

=> x= 4             Vậy x=4

b, (2x-26):12=25

=> 2x-26=300

=> 2x=326

=> x=163           Vậy x= 163

c, 234:( 5x+28)=3

=> 5x+28=78

=> 5x=50

=> x= 10            Vậy x= 10

d, 529: (72-7x)=23

=> 72-7x=23

=> 7x=49

=> x= 7             Vậy x= 7

   Nhớ k cho mik nhé!!!! CẢM ƠN !!!

a)x=45

b)x=270

a) \(40\%\times x+x\times20\%=72\)

       \(\left(40\%+20\%\right)\times x=72\)

                             \(60\%\times x=72\)

                                \(0,6\times x=72\)

                                             \(x=72:0,6\)

                                              \(x=120\)

b) \(x-20\%\times x=216\)

    \(x\times\left(1-20\%\right)=216\)

                   \(x\times80\%=216\)

                      \(x\times0,8=216\)

                                    \(x=216:0,8\)

                                     \(x=270\)