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Tìm số tự nhiên x, biết rằng 162 ⋮ x; 360 ⋮ x và 10 < x < 20 :
A. x = 6
B. x = 9
C. x = 18
D. x = 36
![](https://rs.olm.vn/images/avt/0.png?1311)
Đáp án là C
Vì 162 ⋮ x; 360 ⋮ x ⇒ x ∈ ƯC (162, 360)
Ta có:
162 = 2. 3 4
360 = 2 3 . 3 2 .5
Suy ra, ƯCLN ( 162, 360) = 2. 3 2 = 18
ƯC ( 162, 360) = Ư (18) = {1, 2, 3, 6, 9, 18} ⇒ x ∈ {1, 2, 3, 6, 9, 18}
Vì 10 < x < 20 ⇒ x = 18
![](https://rs.olm.vn/images/avt/0.png?1311)
20+x=40+60
\(\Rightarrow\)20+x=100
\(\Rightarrow\)x=100-20
\(\Rightarrow\)x=80
10+90=40+x
\(\Rightarrow\)100=x+40
\(\Rightarrow\)x=100-40
\(\Rightarrow\)x=60
20 + x = 40 + 60
=> 20 + x = 100
=> x = 100 - 20
=> x = 80
10 + 90 = 40 + x
=> 100 = 40 + x
=> x = 100 - 40
=> x = 60
![](https://rs.olm.vn/images/avt/0.png?1311)
=>(X+X+....+X)+(2+4+...+20)=360
=>10X+(20+2)*10:2=360
=> 10X+110=360
=> 10X=360-110=250
=>X=250:10
=>X=25
study well
K NHA
CẢM ƠN CẢM BẠN NHIỀU
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`@` `\text {Ans}`
`\downarrow`
`[124 - (20 - 4x)] \div 30 = 40`
`\Rightarrow 124 - (20 - 4x) = 40 \times 30`
`\Rightarrow 124 - (20 - 4x) = 120`
`\Rightarrow 20- 4x = 124 - 120`
`\Rightarrow 20 - 4x = 4`
`\Rightarrow 4x= 20 -4`
`\Rightarrow 4x = 16`
`\Rightarrow x = 16 \div 4`
`\Rightarrow x = 4`
Vậy, `x = 4.`
[124-(20-4.x)]:30=40
=>124-(20-4x)=40*30
=>124-(20-4x)=120
=>20-4x=124-120
=>20-4x=4
=>4x-20-4
=>4x=16
=>x=16:4
=>x=4
![](https://rs.olm.vn/images/avt/0.png?1311)
a,\(\left(\frac{7}{5}-2x\right).\frac{40}{20}=\frac{8}{14}\)
\(\Rightarrow\left(\frac{7}{5}-2x\right).2=\frac{4}{7}\)
\(\Rightarrow\frac{7}{5}-2x=\frac{4}{7}:2\)
\(\Rightarrow\frac{7}{5}-2x=\frac{2}{7}\)
\(\Rightarrow2x=\frac{7}{5}-\frac{2}{7}\)
\(\Rightarrow2x=\frac{39}{35}\)
\(\Rightarrow x=\frac{39}{35}:2\)
\(\Rightarrow x=\frac{39}{70}\)
b, \(\frac{7}{2}.x-20\%.x=-4\)
\(\Rightarrow x\left(\frac{7}{2}-20\%\right)=-4\)
\(\Rightarrow x\left(\frac{7}{2}-\frac{1}{5}\right)=-4\)
\(\Rightarrow x\frac{7}{10}=-4\)
\(\Rightarrow x=-4:\frac{7}{10}\)
\(\Rightarrow x=-\frac{40}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có: \(B\left(9\right)=\left\{0,9,18,27,36,45,54,....\right\}\)
mà \(20< x< 40\)
\(\Rightarrow x\in\left\{27,36\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có: \(B\left(9\right)=\left\{0;9;18;27;36;45;....\right\}\)
mà 20<x<40
=>\(x\in\left\{27,36\right\}\)
(-360):x+20=-40
=>(-360):x=-40-20=-60
=>360:x=60
=>x=360/60=6
(-360) ⋮ x + 20 = -40
=> -360 : x = -60
=> x = 6