A

a

Chọn A

a) 172 + 10 x 2 = 170 +20 = 192

b) 10 x 2 + 300 = 20 + 300 = 320

c) 69 – 54 : 6 = 69 – 9 = 60

d) 900 + 9 x 10 = 900 +90 = 990

e) 20 x 6 + 70 = 120 + 70 = 190

f) 72 + 300 x 3 = 72 + 900 = 972

a) x = 44.             

b) x = 40.            

c) x = 95.             

d) x = 10.

a) x - 120: 30 = 40

    x    -40        =40

              x        =40+40

              x        =80

b) (x + 120) : 20 = 8

    (x+ 120)         = 8x20

     x+120           =160

     x                   = 160-120

     x                  = 40

c) (x + 5). 3 = 300

     x+5=300:3

     x+5=100

     x=100-5

     x=95

d) x.2 + 21 : 3= 27

    x.2   +7=27

      x.2   = 27-7

    x.2= 20

      x=20:2

      x=10

a) \(x-285\div35=5\times54\)

\(x-\dfrac{57}{7}=270\)

\(x=\dfrac{1947}{7}\)

b) \(\left(x+120\right)\div20=8\)

\(x+120=160\)

\(x=40\)

c) \(\left(x+5\right)\times3=300\)

\(x+5=100\)

\(x=95\)

d) \(\left(x+100\right)\times4=800\)

\(x+100=200\)

\(x=100\)

a) \(x-285:35=5x54\)

\(x-\dfrac{57}{7}=270\)

\(x=270+\dfrac{57}{7}=\dfrac{1890}{7}+\dfrac{57}{7}=\dfrac{1947}{7}\)

b) \(\left(x+20\right):20=8\)

\(\left(x+20\right)=8x20\)

\(x+20=160\)

\(x=160-20=140\)

c) \(\left(x+5\right)x3=300\)

\(x+5=300:3\)

\(x+5=100\)

\(x=100-5=95\)

d) \(\left(x+100\right)x4=800\)

\(x+100=800:4\)

\(x+100=200\)

\(x=200-100=100\)

\(12,45\times x-0,45\times x+x=3,9.\)

\(\Leftrightarrow x\times\left(12,45-0,45+1\right)=3,9.\)

\(\Leftrightarrow x\times13=3,9.\)

\(\Leftrightarrow x=0,3.\)

Vậy \(x=0,3.\)

 x như thế nào với 45, 110 và 75 ??

Chọn B

C

Chọn B

B