tính nhanh : 25+16+72+28+75+84
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 11 + 28 + 24 + 16 + 112 + 9
= ( 11 + 9 ) + ( 28 + 112 ) + ( 24 + 16 )
= 20 + 140 + 40
= 200
b) 75 - 13 - 17 - 25
= ( 75 - 25 ) - 13 - 17
= 50 - 13 - 17
= 20
![](https://rs.olm.vn/images/avt/0.png?1311)
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) \(\left(-456\right)-\left(67-456\right)\)
\(=-456-67+456\)
\(=\left(456-456\right)-67\)
\(=67\)
![](https://rs.olm.vn/images/avt/0.png?1311)
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
\(...=45-58-45+58-3=-3\)
\(...=-57+12+3+57=15\)
\(...=24+30-24-30+8=8\)
\(...=12+19-12+8-19=8\)
\(...=47+53-47-53=0\)
\(...=-28+32+28-34=-2\)
\(...=15-72-15+72=0\)
\(...=20-46-25+46=-5\)
\(=...28+32-28-32+5=5\)
\(...=-75-49+75+49-12=-12\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1: Ta có: \(2155-\left(174+2155\right)+\left(-68+174\right)\)
\(=2155-174-2155-68+174\)
=-68
2) Ta có: \(-25\cdot72+25\cdot21-49\cdot25\)
\(=-25\cdot\left(72-21+49\right)\)
\(=-25\cdot100=-2500\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{72\times202\times28}{303\times63\times16}=\dfrac{8\times9\times2\times101\times4\times7}{7\times9\times3\times101\times16}=\dfrac{\left(8\times2\times4\right)\times\left(9\times101\times7\right)}{\left(16\times3\right)\times\left(9\times101\times7\right)}=\dfrac{4}{3}\)
\(\dfrac{72\cdot202\cdot28}{303\cdot63\cdot16}=\dfrac{2^3\cdot9\cdot101\cdot2\cdot7\cdot4}{101\cdot3\cdot7\cdot9\cdot2^3\cdot2}\)
\(=\dfrac{4}{3}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) ( − 4 ) .13. ( − 250 ) = ( − 4 ) . ( − 250 ) .13 = 1000.13 = 13000
b) ( − 37 ) .84 + 37. ( − 16 ) = ( − 37 ) .84 + ( − 37 ) .16 = ( − 37 ) . ( 84 + 16 ) = ( − 37 ) .100 = − 3700
c) 25. ( − 5 ) .4. ( − 20 ) = 25.4. ( − 5 ) . ( − 20 ) = 100.100 = 10000
d) ( − 48 ) .72 + 36. ( − 304 ) = ( − 48 ) .2.36 + 36. ( − 304 ) = ( − 96 ) .3 + 36. ( − 304 )
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left[\left(6\times x-72\right):2-84\right]\times28=5628\)
\(\left(6\times x-72\right):2-84=5628:28\)
\(\left(6.x-72\right):2-84=201\)
\(\left(6.x-72\right):2=201+84\)
\(\left(6.x-72\right):2=285\)
\(6.x-72=285.2\)
\(6.x-72=570\)
\(6.x=570+72\)
\(6.x=642\)
\(x=642:6\)
\(x=107\)
[(6xX-72):2-84]x28=5628
⇒ (6xX-72):2-84=5629:28=201
⇒ (6xX-72):2=201+84=285
⇒ 6xX-72=285x2=570
⇒ 6xX=570+72=642
⇒ X= 642:6=107
⇒ X=107
300 nhé
25+16+72+28+75+84
=(25+75)+(16+84)+(72+28)
=100+100+100
=300