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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
(-315) + 135 +( - 315 + 685)
= -315 + 135 - 315 + 685
= ( 135 + 685 ) - ( 315+315)
= 820 - 630
= 190
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 2 : Tính nhanh
a) 315 + [135+(-315)+(-35)
=315+135+(-315)+(-35)
=[315 + (-315) ] +[135+(-35) ]
= 100
b) 815 + [95+(-815)+(-45)
=815+95+(-815)+(-45)
=[815+(-815)] + [ 95 +(-45)]
= 50
Chúc bạn học tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
a ) x : 3 1 5 = 1 1 2 ⇒ x = 1 1 2 .3 1 5 = 3 2 . 16 5 = 24 5
b ) 2 2 5 : x = − 1 3 5 ⇒ x = 2 2 5 : − 1 3 5 = 12 5 : − 8 5 = − 3 2 .
![](https://rs.olm.vn/images/avt/0.png?1311)
2,
a) \(315-\left(135-x\right)=215\)
\(\Rightarrow135-x=315-215\)
\(\Rightarrow135-x=100\)
\(\Rightarrow x=135-100\)
\(\Rightarrow x=35\)
b) \(x-320:32=25\cdot16\)
\(\Rightarrow x-10=5^2\cdot4^2\)
\(\Rightarrow x-10=20^2\)
\(\Rightarrow x-10=400\)
\(\Rightarrow x=410\)
c) \(3\cdot x-2018:2=23\)
\(=3\cdot x-1009=23\)
\(\Rightarrow3\cdot x=1032\)
\(\Rightarrow x=1032:3\)
\(\Rightarrow x=344\)
d) \(280-9\cdot x-x=80\)
\(\Rightarrow280-x\cdot\left(9+1\right)=80\)
\(\Rightarrow280-10\cdot x=80\)
\(\Rightarrow10\cdot x=280-80\)
\(\Rightarrow10\cdot x=200\)
\(\Rightarrow x=20\)
e) \(38\cdot x-12\cdot x-x\cdot16=40\)
\(\Rightarrow x\cdot\left(38-12-16\right)=40\)
\(\Rightarrow x\cdot10=40\)
\(\Rightarrow x=40:10\)
\(\Rightarrow x=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
C) x-135=315-450
X-135=-135
X=0
D) 346+(210-x)=556
X-210=346-556
X-210=-210
X=0
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 2316 + 115 = 2431
b) (-315)+ (-15) = -330
c) (-215)+215 = 0
d) (-200)+200 = 0
\(315+135+\left(-315\right)+\left(-15\right)\)
\(=315+135-315-15\)
\(=\left(315-315\right)+\left(135-15\right)\)
\(=0+120\)
\(=120\)
315 + 135 +(-315) + (-15)
= [315+(-135)] + [135 + (-15)]
= 0 + 120
= 120
k mk nha bn