a) 87 x (-78) + 78 x 31 - 78 x (-156)

= (-87 + 31 + 156) x 78

=  100 x 78

= 7800

b) -178 x (-35 - 78) - 78 x (178 + 35)

= -178 x (-113) - 78 x 213

= 20114 - 16614

= 3500

Đáp án cần chọn là: B

Đáp án là B

Ta có:  17 8 : 17 3  =  17 8 - 3  =  17 5

1: -20<x<21

=>\(x\in\left\{-19;-18;...;19;20\right\}\)

Tổng là (-19)+(-18)+...+18+19+20=20

2: -18<=x<=17

=>\(x\in\left\{-18;-17;...;16;17\right\}\)

Tổng là (-18)+(-17)+...+16+17

=(-18)

3: -27<x<=27

=>\(x\in\left\{-26;-25;...;24;25;26;27\right\}\)

Tổng là 27

4: |x|<=3

=>\(x\in\left\{0;1;-1;2;-2;3;-3\right\}\)

Tổng là 0

5: |-x|<5

=>|x|<5

=>\(x\in\left\{0;1;-1;2;-2;3;-3;4;-4\right\}\)

Tổng là 0

a) (3x-12) :8 +10= 13

<=> (3x-12):8 = 13-10 = 3

<=> 3x-12 = 3 .8 = 24

<=> 3x = 24+12=36

<=> x=36:3=12

b) (x+5).8-20 = 60

<=> (x+5) .8 = 60+20=80

<=> x+5 = 80:8 = 10

<=> x=10-5 = 5

c) 3.[35+(x-10)]-375 = 0

<=> 3.[35+(x-10)] = 0 +375=375

<=> 35+(x-10) = 375 :3 = 125

<=> x-10 = 125-35=90

<=> x = 90+10 = 100

d) ( 158x+173-24) :35 = 81

<=> 158x+149 = 81 . 35 = 2835

<=> 158x = 2835 -149= 2686

<=> x= 2686 : 158 = 17

e) x - 140 : 35 = 0

<=> x-4 = 0

<=> x=0+4 = 4

(3x - 12 ) : 8 + 10 = 13 

(3x - 12 ) : 8 = 13 - 10 = 3

(3x - 12 ) = 3 x 8 = 24

3x = 24 - 12 = 12

x =13 : 3 = 4

( x + 5 ) 

yx(15+35)=150

yx50          =150

y                =150:50=3

yx5=713-173

yx5=540

y   =540:5=108

a. y x (15+35)=150

y x 50 =150

y         = 150 : 50

y         = 3

b.    y x 5    = 713-173

       y x 5    = 540

       y          =540:5

       y          = 108

\(1158-35\cdot\left(x+1\right)=178\)

\(35\cdot\left(x+1\right)=980\)

\(35\cdot x=945\)

\(x=27\)

\(1158-35.\left(x+1\right)=178\)

\(35.\left(x+1\right)=1158-178\)

\(35.\left(x+1\right)=980\)

\(x+1=980:35\)

\(x+1=28\)

\(x=28-1\)

\(x=27\)

1158-35.(x+1)=178

35.(x+1)         =1158- 178

35.(x+1)         =980

      x+1           =980:35

       x+1         = 28

       x             =28-1

        x             =27

a/ (3x -12 ):8+10=13

 <=>(3x-12):8=3

<=>3x-12=24

<=>3x=36

<=>x=12

b/(x+5)x8-20=60

<=>(x+5)x8=80

<=>x+5=80:8

<=>x+5=10

x=5

c/3x[35+(x-10)]-375=0

<=>3x[35+(x-10)]=375

<=>35+(x+10)=125

<=>x+10=90

x=80

d/(158x+173-24):35=81

<=>158x+173-24=2835

<=>158x+173=2859

<=>158x=2686

<=>x=17

e/x-140:35=0

<=>x-140=0

<=>x=140+0

x=140

a)  ( 3x - 12 ) : 8 + 10 = 13

=>  (3x - 12) : 8 = 3

=>  3x - 12 = 24

=> 3x = 12

=> x = 4

a)  ( 3x - 12 ) : 8 + 10 = 13

=>  (3x - 12) : 8 = 3

=>  3x - 12 = 24

=> 3x = 12

=> x = 4