Tìm x:

a) \(2x-12-x=0\)

\(2x-x=12\)

\(x=12\)

b) \(2x+69\cdot2=69\cdot4\)

\(2x=69\cdot4-69\cdot2\)

\(2x=69\cdot2\)

\(x=69\cdot2:2\)

\(x=69\)

Tính nhanh:

\(769\cdot85-769-75=769\cdot84-75\)

(sao tính nhanh được)

a) 2*x - 12- x = 0

 2*x - x - 12 = 0

 x * ( 2 - 1) - 12 = 0

 x = 12

b) 2 * x + 69 *2 = 69 * 4

    2 * ( x + 69 ) = 276

           x + 69   = 276/2

           x + 69   = 138

           x          = 69

769 * 85 - 769 - 75

= 769*(85-75)

=769*10

=7690

a) 2 x 39 x 5

= 39 x (2 x 5)

= 39 x 10 = 390

b) 302 x 16 + 302 x 4

= 302 x ( 16 +4)

= 302 x 20 = 6040

c) 769 x 85 – 769 x 75

= 769 x (85 – 75)

= 769 x 10 = 7690

A ) 2 x 39 x 5 = 2 x 5 x 39 = 10 x 39 = 390

B ) 302 x 16 + 302 x 4 

=302 x (16 + 4)

=302 x 20

=6040

C ) 769 x 85 - 769 x 75 = 769 x(85 - 75)=769 x 10 = 7690

\(a,\) \(2\times39\times5\)

   \(=\left(2\times5\right)\times39\)

     \(=10\times39\)

     \(=390\)

\(b,\) \(302\times16+302\times4\)

    \(=302\times\left(16+4\right)\)

     \(=302\times20\)

      \(=\left(300+2\right)\times20\)

      \(=300\times20+2\times20\)

       \(=6000+40\)

        \(=6040\)

\(c,\) \(769\times85-769\times75\)

    \(=769\times\left(85-75\right)\)

     \(=769\times10\)

      \(=7690\)

  Cách này không cần dùng máy tính nhẩm cũng ra!

\(a,\) \(2\times39\times5\)

   \(=\left(2\times5\right)\times39\)

     \(=10\times39\)

     \(=390\)

\(b,\) \(302\times16+302\times4\)

    \(=302\times\left(16+4\right)\)

     \(=302\times20\)

      \(=\left(300+2\right)\times20\)

      \(=300\times20+2\times20\)

       \(=6000+40\)

        \(=6040\)

\(c,\) \(769\times85-769\times75\)

    \(=769\times\left(85-75\right)\)

     \(=769\times10\)

      \(=7690\)

A, 2 x 26 x 5 =( 5 x 2) x 26

10 x 26

=260                   

 b,4 x 37 x 25 =( 4 x 25) x 26

= 100 x 26

= 3700           

 c, 25 x 5 x 4 x 27 x 2 =( 25 x 4 ) x ( 2x 5) x 27

= 100 x 10 x 27 

= 1000x 27 

=27000

d,28 x 64 + 28 x 36 = 28 x ( 64 + 36 )

= 28 x 100

=2800

 e, 769 x 85 - 769 x 75  = 769 x ( 85 - 75 )

=769 x 10

=7690

f, 56 x 37 + 56 x 63 = 56 x ( 37 + 63 )

= 56 x 100

=5600

a. = 26 x (2 x 5)

   = 26 x 10 =260

b.=( 25x4) x37

   =100 x37=3700

c.=(25x4) x(5x2) x27

   =100 x10 x27

   = 27000

d.=28 x( 64+36)

   =28 x100

  = 2800

e.=769 x( 85-75)

    =769 x10 =7690

f. =56 x(37 +63)

  =56 x100

= 5600

769 x  85 – 769 x 75 = 769 × (85 – 75) = 769 × 10 = 7690

Bài 1:

769 x 85 – 769 x 75

=769x(85-75)

=769x10

=7690

Bài 1:
\(769\times85-769\times75\\ =769\times\left(85-75\right)\\ =769\times10\\ =7690\)

Bài 2:
Trung bình mỗi lớp có số học sinh là:

\(\left(35\times2+33\times2\right):\left(2+2\right)=34\left(học.sinh\right)\)

769 x 85 - 769 x 75 = 769 x ( 85 - 75 )

                                = 769 x 10 = 7690.

769 x 85 - 769 x 75
= 769 x (85 - 75)

= 769 x 10

= 7690

769 x 85 - 769 x 75=769x(85-75)

=769x10=7690

= 769 x (85 - 75)

= 769 x 10

= 7690

769 x 85 – 769 x 75

= 769 x (85 – 75)

= 769 x 10 = 7690