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2) 
3) 
4) 
a ) 5 . ( - 2 ) . ( - 3 )
= ( - 10 ) . ( - 3 )
= 30
b ) ( - 20 ) + ( - 12 ) - ( - 4 )
= ( - 20 ) + ( - 12 ) + 4
= ( -20 ) + [ ( - 12 ) + 4 ]
= ( - 20 ) + ( - 8 )
= - 28
c . 78 . 45 - 145 . 78
= 78 . ( 45 - 145 )
= 78 . ( - 100 )
= - 7800
1) 39×51+39×49=39x(51+49)=39x100=3900
2. phân tích 100 thành 50 r lm như câu 1
1. = 39 x (51 + 49)
= 39 x 100
= 3900
2. = 50 x 2 x 31 + 100 x 19
= 100 x 31 + 100 x 19
= 100 x (31 + 19)
= 100 x 50
= 5000
45-58+(-45)+(+58)-3=45-58-45+58-3=(45-45)+(58-58)-3=-3
(-57)-(-12)+3-(-57)=-57+12+3+57=(-57+57)+12+3=15
-(-24)-(-30)+(-24)-30+8=24+30-24-30+8=(24-24)+(30-30)+8=8
-(-12)+(+19)-(+12)+8-19=12+19-12+8-19=(12-12)+(19-19)+8=8
47-(-53)+(-47)-(+53)=47+53-47-53=(47-47)+(53-53)=0
-(+28)+32-(-28)+(-34)=-28+32+28-34=(-28+28)-(34-32)=-2
15-(+72)+(-15)+(+72)=15-72-15+72=(15-15)+(72-72)=0
20-(+46)+(-25)-(-46)=20-46-25+46=(20-25)+(46-46)=-5
28-(-32)+(-28)-32+5=28+32-28-32+5=(28-28)+(32-32)+5=5
-75+(-49)+(+75)+49-12=-75-49+75+49-12=(-75+75)+(49-49)-12=-12
\(...=45-58-45+58-3=-3\)
\(...=-57+12+3+57=15\)
\(...=24+30-24-30+8=8\)
\(...=12+19-12+8-19=8\)
\(...=47+53-47-53=0\)
\(...=-28+32+28-34=-2\)
\(...=15-72-15+72=0\)
\(...=20-46-25+46=-5\)
\(=...28+32-28-32+5=5\)
\(...=-75-49+75+49-12=-12\)
Bài 2:
a. $=62-81-12+59-9=(62-12)+(59-9)-81$
$=50+50-81=100-81=19$
b. $=39+13-26-62-39=(39-39)+13-(26+62)$
$=0+13-88=-(88-13)=-75$
c. $=(32-42)+(36-34)+(40-38)=10+2+2=14$
d. $=92-55+8-45=(92+8)-(55+45)=100-100=0$
Bài 1:
a. $=(387-87)-224=300-224=76$
b. $=-(75+35)+379=-110+379=379-110=269$
c. $=(11+15)-(13+17)=25-30=-5$
d. $=(31-21)-(27-24)=10-3=7$
1: Ta có: \(2155-\left(174+2155\right)+\left(-68+174\right)\)
\(=2155-174-2155-68+174\)
=-68
2) Ta có: \(-25\cdot72+25\cdot21-49\cdot25\)
\(=-25\cdot\left(72-21+49\right)\)
\(=-25\cdot100=-2500\)
a) \(\left(-25\right).5.\left(-4\right).2\)
\(=\left[\left(-25\right).\left(-4\right)\right].\left(2.5\right)\)
\(=100.10=1000\)
b) \(\left(-456\right)-\left(67-456\right)\)
\(=-456-67+456\)
\(=\left(456-456\right)-67\)
\(=67\)
a) ((-25).(-4)).5.2
=100.10
=1000
b) (-456)-67+456
=(-456)+(-67)+456
=0+-(-67)
=-67
c)78.45+-145.78
=78.(45+145)
=78.190
=Tự làm