a,

\(B=\left(\dfrac{5}{7}\cdot0,6-5:\dfrac{7}{2}\right)\cdot\left(40\%-1,4\right)\cdot\left(-2\right)^3\\ =\left(\dfrac{5}{7}\cdot\dfrac{3}{5}-5\cdot\dfrac{2}{7}\right)\cdot\left(\dfrac{2}{5}-\dfrac{7}{5}\right)\cdot\left(-8\right)\\ =\left(\dfrac{3}{7}-\dfrac{10}{7}\right)\cdot\left(-1\right)\cdot\left(-8\right)\\ =\left(-1\right)\cdot\left(-1\right)\cdot\left(-8\right)\\ =\left(-8\right)\)

b,

\(\dfrac{1}{2}\cdot x+\dfrac{3}{5}\cdot\left(x-2\right)=3\\ \dfrac{1}{2}x+\dfrac{3}{5}x-\dfrac{6}{5}=3\\ x\left(\dfrac{1}{2}+\dfrac{3}{5}\right)=3+\dfrac{6}{5}\\ x\cdot\dfrac{11}{10}=\dfrac{21}{5}\\ x=\dfrac{21}{5}:\dfrac{11}{10}\\ x=\dfrac{42}{11}\\ Vậy......\)

B)

( x + 4/3 ) * 7/4 = 5 - 7/6

( x + 4/3) * 7/4 = 5/1 - 7/6

( x + 4/3) * 7/4 = 30/6 - 7/6

( x + 4/3) * 7/4 = 23/6 

( x + 4/3)        = 23/6 : 7/4

( x+ 4/3)         = 23/6 . 4/7

( x+ 4/3)         = 46/21

  x                 = 46/21 - 4/3

  x                  = 46/21 - 28/21

 x                 =  18/21 = 6/7
Tk vs kb hộ mk nha! thank u 

may cau khac ko kho lam dau chi co cau d thoi.

(100%-50%+40%):x=18%+30%:x

90%:x=18%+30%:x

18%=90%:x-30%:x

18%=60%:x

X=60%:18%

x=..................................................................................................

xong roi do  a cho minh nhe

a, 5(x – 7) = 0

x – 7 = 0

x = 7

b, 95 – 5(x+2) = 45

5(x+2) = 40

x+2 = 8

x = 6

c,  6 2 x + 2 3 + 40 = 100

6(2x+8) = 60

2x+8 = 10

x = 1

d, 3(3x+9)+6 = 96

3(3x+9) = 90

3x+9 = 30

3x = 27

x = 9

e,  2 6 + 5 + x = 3 4

5+x = 81–64

5+x = 17

x = 12

a) 2² ( x + 3² ) - 5 = 55

=>4(x+9)-5=55

=>4(x+9)=60

=>x+9=15

=>x=6

b)7 ( x + 5² ) - 20 = 190

=>7(x+25)=210

=>x+25=30

=>x=5

c)6 ( x + 2³ ) + 40 = 100

=>6(x+8)+40=100

=>6(x+8)=60

=>x+8=10

=>x=2

a)6

b)5

c)2

a: \(\frac{4^5\cdot10\cdot5^6+25^5\cdot2^8}{2^8\cdot5^4+5^7\cdot2^5}\)

\(=\frac{2^{10}\cdot2\cdot5\cdot5^6+5^{10}\cdot2^8}{2^8\cdot5^4+5^7\cdot2^5}=\frac{2^8\cdot5^7\left(2^3+3^3\right)}{2^5\cdot5^4\left(2^3+3^3\right)}\)

\(=2^3\cdot5^3=10^3=1000\)

b: \(149-\left(35:x+3\right)\cdot17=13\)

=>\(\left(35:x+3\right)\cdot17=149-13=136\)

=>35:x+3=136:17=8

=>35:x=8-3=5

=>\(x=\frac{35}{5}=7\)

c: \(121:11-\left(4x+5:3\right)=4\)

=>11-(4x+5/3)=4

=>4x+5/3=11-4=7

=>\(4x=7-\frac53=\frac{21}{3}-\frac53=\frac{16}{3}\)

=>\(x=\frac{16}{3}:4=\frac43\)

d: \(720:\left\lbrack41-\left(2x-5\right)\right\rbrack=40\)

=>\(41-\left(2x-5\right)=\frac{720}{40}=18\)

=>2x-5=41-18=23

=>2x=28

=>\(x=\frac{28}{2}=14\)

e: Sửa đề: (x+1)+(x+2)+(x+3)+...+(x+100)=5700

=>100x+(1+2+3+...+100)=5700

=>\(100x+100\cdot\frac{101}{2}=5700\)

=>x+50,5=57

=>x=57-50,5

=>x=6,5

2:

a: =>2/3:x=1,4-2,4=-1

=>x=-2/3

b: =>x/5=25/30-19/30=6/30=1/5

=>x=1

3:

Số học sinh giỏi là 40*1/4=10 bạn

Số học sinh khá là 30*3/5=18 bạn

Số học sinh TB là 30-18=12 bạn

a)(3/4-5/6+7/12).(-12/7)=1/2.(-12/7)

=6/7

b)1,4.15/49-(4/5+2/3):11/5=1,4.15/49-22/15:11/5

=3/7-2/3=-5/21

(3/4-5/6+7/12)×(-12/7)

=(9/12-10/12+7/12)×(-12/7)

=(-1/12+7/12)×(-12/7)

=6/12×(-12/7)

=1/2×(-12/7)

=-12/14

=-6/7