315x55 +315 x45 b) 678 x125 – 25 x678
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a) \(4\times378\times25\)
\(=\left(25\times4\right)\times378\)
\(=100\times378\)
\(=37800\)
b) \(214\times53-214\times45\)
\(=214\times\left(53-45\right)\)
\(=214\times8\)
\(=1712\)
a) \(4\times378\times25\)
\(=4\times25\times378\)
\(=100\times378\)
\(=37800\)
b) \(214\times53-214\times45\)
\(=214\times\left(53-45\right)\)
\(=214\times8\)
\(=1712\) ( Thuận tiện chỗ nào? )
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, 2 x 7,65 x 5
= ( 2 x 5 ) x 7,65
= 10 x 7,65
= 76,5
b, 25 x 1,9 x 4
= ( 25 x 4 ) x 1,9
= 100 x 1,9
= 190
c , 6,92 x 8 x 125
= 6,92 x ( 125 x8 )
= 6,92 x 1000
= 6920
d, 15,7 x 8 + 15,7 x2
= 15,7 x ( 8 + 2 )
= 15,7 x 10
= 157
![](https://rs.olm.vn/images/avt/0.png?1311)
4 × 125 × 25 × 8
= (4 × 25) × (125 × 8)
= 100 × 1000
= 100 000
2 × 8 × 50 × 25 × 125
= (2 × 50) × (8 × 125) × 25
= 100 × 1000 × 125
= 12 500 000
2 × 3 × 4 × 5 × 50 × 25
= (2 × 50) × (4 × 25) × (3 × 5)
= 100 × 100 × 15
= 150 000
25 × 20 × 125 × 8 - 8 × 20 × 5 × 125
= 8 × 125 × 20 × (25 - 5)
= 1000 × 20 × 20
= 400 000
- (25 x 4) x (125 x8)=100 x 1000 =100000
- (50 x 2) x (8 x 125) x 25=100 x 1000 x 25 =2500000
- (2 x 50 ) x (4 x 25) x (3 x5)=100 x 100 x 15=150000
- 25 x 20 x125 x 8 - 5
= (20 x 5) x (125 x 8) -25=100 x 1000 -5 =100000 - 5 =99995
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 315 + 2x = x+115
<=> 2x-x = 115-315
<=> x = -200
Vậy x= -200
b) 25-(30-x)=25-(-12+125)
<=> 25-30+x = -88
<=> -5 + x =-88
<=> x = -83
Vậy x=-83
a=31500
b=67800
a) 315 ✖55 + 315✖45 b) 678✖125-25✖678
= 315✖(55+45) =678✖(125-25)
=315 ✖ 100 =678✖100
=31500 =67800