`#040911`

`b,`

`6 \times 1235 \times 20 - 5 \times 235 \times 24`

`= 6 \times (1000 + 235) \times 20 - 5 \times 235 \times 24`

`= 120 \times 1000 + 120 \times 235 - 120 \times 235`

`= 120 \times 1000 + 0`

`= 120000`

`c,`

\((145 \times 99+145)-143 \times 101-143\)

`=`\(145 \times 99 + 145 - 143 \times 101 - 143\)

`=`\(145 \times (99 + 1) - 143 \times (101 - 1)\)

`=`\(145 \times 100 - 143 \times 100\)

`=`\(100 \times (145 - 143)\)

`=`\(100 \times 2=200\)

`d,`

`54 \times 47 - 47 \times 53 - 20 - 27`

`= 54 \times 47 - 47 \times 53 - (20 + 27)`

`= 54 \times 47 - 47 \times 53 - 47`

`= 47 \times (54 - 53 - 1)`

`= 47 \times 0=0`

 (145 x 99 + 145) - ( 143 x 101)

= (145 x (99+1) - (143 x (100+1))

=( 145x100 ) - (143 x 100 + 143 x 1)

=   14500  - ( 14300+143)

=  57

a, 8 x 247 x 3 + 6 x 573 x 4 

=24 x 247 + 24 x 573

=24 x ( 247 + 573 )

=24 x 820

=19680 ( mik nghĩ là bạn viết sai đề )

b,  6 x 1235 x 20 - 5 x 235 x 24

= 120 x 1235 - 120 x 235

= 120 x (1235 - 235)

=120 x 1000

=120000

c, ( 145 x 99 + 145 ) - ( 143 x 102 - 143 )

= [145 x ( 99+1)] - [ 143 x (102 - 1)]

= (145 x 100) - ( 143 x 100) 

= (145 - 143) x 100

= 2 x 100

=200

d, 54 x 47 - 47 x 53 - 20 - 27

= 47 x (54 -53) - 20 - 27

= 47 x 1 - 20 - 27

= 47 - (20 + 27)

=47 - 47

=0

thật ra đề bài khó hơn nhưng tui cho dễ thôi

a)3906237648

b)-5019

Học tốt! k nha.

 (145x99+145)-(143x101)

=(145x(99+1))-(143x(100+1))

=(145x100)-(143x100+143x1)

=   14500  -(14300+143)

=   14500-14443

=  57

k đi 

=

a.45+45+45+45+15+15+15+15=45×4+15×4=4×(45+15)=4×60=240

125+125+125+125-25-25-25-25=125×4-25×4=4×(125-25)=4×100=400

8x427x3+6x573x4

=24x427+24x573

= 24x( 427+573)

=24x 1000

=24000