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a) \(215+x=400\)
\(\Rightarrow x=400-215\)
\(\Rightarrow x=185\)
b) \(12,5-2x=\dfrac{1}{5}\)
\(\Rightarrow2x=12,5-\dfrac{1}{5}\)
\(\Rightarrow2x=\dfrac{123}{10}\)
\(\Rightarrow x=\dfrac{123}{10}:2\)
\(\Rightarrow x=\dfrac{123}{20}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
0,25 x X = 6- \(3\frac{1}{4}\)
0,25 x X = 6 - 13/4
0,25 x X = 11/4
0,25 x X = 2,75
X = 2,75: 0,25
X= 11
![](https://rs.olm.vn/images/avt/0.png?1311)
1) 2,75 - 5/6 × 2/5 = 2,75 - (5/6) × (2/5) = 2,75 - 1/3 = 2,75 - 0,33 = 2,42
2) 1,25 - (5/6 - 0,75) - 3/5 = 1,25 - (5/6 - 0,75) - 3/5 = 1,25 - (5/6 - 3/4) - 3/5 = 1,25 - (5/6 - 9/12) - 3/5 = 1,25 - (10/12 - 9/12) - 3/5 = 1,25 - 1/12 - 3/5 = 1,25 - 0,08 - 0,6 = 1,25 - 0,68 = 0,57
3) 4/9 × 0,75 + 8/5 + 3,125 = (4/9) × 0,75 + 8/5 + 3,125 = 0,44 + 8/5 + 3,125 = 0,44 + 1,6 + 3,125 = 0,44 + 4,725 = 5,165
4) 1,125 - 4/7 - 0,12 = 1,125 - (4/7) - 0,12 = 1,125 - 0,57 - 0,12 = 0,435 - 0,12 = 0,315
5) (1/3 + 0,4) × 3,5 + (1/6 + 0,75) × 6/5
![](https://rs.olm.vn/images/avt/0.png?1311)
2/3xX-1/4:(11/2-3/4)=1/6
2/3xX:19/4=1/6
2/3xX=1/6x19/4
2/3xX=19/24
X=19/24:2/3
X=19/16
chắc luôn
Tìm x biết:
a) (15 × 19 – x – 0,15):0,25 = 15 : 0,25
b)\(2\frac{2}{3}-x=\frac{1}{3}\cdot\frac{6}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) (15 x 19 - x - 0,15) : 0,25 = 15 : 0,15
(285 - x - 0,15) : 0,25 = 60
(285 - x - 0,25) = 60 : 0,25
( 285 - x - 0,25) = 15
285 - x = 15 + 0,25
285 - x = 15,25
x = 285 - 15,25
x = 269,75
![](https://rs.olm.vn/images/avt/0.png?1311)
X : 0,25 - X x 0,25 - X x 3/4 = 7.5
X x 4 - X x 0,25 - X x 0,75 = 7,5
X x (4-0,25-0,75) = 7,5
X x 3 = 7,5
X = 7,5 : 3
X = 2,5
3/3 - 1/4.x=0,25
=> 1-1/4x=0,25
1/4x=1-0,25
1/4x=0,75
x=0,75:1/4
x=3
Vậy x=3