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\(a.\dfrac{12+x}{42}=\dfrac{35}{42}\Leftrightarrow12+x=35\Leftrightarrow x=23\)
\(b.\dfrac{25-x}{40}=\dfrac{3}{8}\Leftrightarrow\dfrac{25-x}{40}=\dfrac{15}{40}\Leftrightarrow25-x=15\Leftrightarrow x=10\)
\(c.\dfrac{13+x}{20}=\dfrac{3}{4}\Leftrightarrow\dfrac{13+x}{20}=\dfrac{15}{20}\Leftrightarrow13+x=15\Leftrightarrow x=2\)
\(d.\dfrac{23-x}{25}=\dfrac{20}{25}\Leftrightarrow23-x=20\Leftrightarrow x=3\)
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a, x+4/7=7/4-1/4
x + 4/7 = 6/4
x = 6/4 - 4/7
x = 26/28
b, 9/2+(x-3/4)=25/4
x - 3/4 = 25/4 - 9/2
x - 3/4 = 7/4
x = 7/4 + 3/4
x = 10/4
a, x+4/7=7/4-1/4
x+4/7= 3/2
x = 3/2-4/7= 13/14
b,9/2+(x-3/4)=25/4
x-3/4 = 25/4 - 9/2 = 7/4
x= 7/4 + 3/4 = 5/2
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1.8100
2. 34 x 18 + 18 x 66
= 18 x ( 34 + 66)
= 18 x 100 = 1800
3. X × ( 8 + 12) = 160 + 20 × 12
= X x 20 = 160 + 240
= X x 20 = 400
X = 400 : 20 = 20
4. X x 12 - X x 2 = 2020
(12 - 2) x X = 2020
10 x X = 2020
X = 2020 : 10 = 202
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\(x\times125-x\times25=37800\\ \Rightarrow x\times\left(125-25\right)=37800\\ \Rightarrow x\times100=37800\\ x=378\)
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14 x \(x\) + \(x\) x 26 = 25
( 14 + 26 ) x \(x\) = 25
40 x \(x\) = 25
\(x\) = 25 : 40
\(x\) = \(\dfrac{5}{8}\)
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\(14\times x+x\times26=25\\ \Rightarrow x\times\left(14+26\right)=25\\ \Rightarrow x\times40=25\\ \Rightarrow x=25:40\\ \Rightarrow x=\dfrac{5}{8}\)
Vậy \(x=\dfrac{5}{8}\)
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124 : x + 24 : x - 48: x = 25
( 124 + 24 - 48 ) : x = 25
100 : x = 25
x = 4
\(124\div x+24\div x-48\div x=25\)
\(\Leftrightarrow\left(124+24-48\right)\div x=25\)
\(\Leftrightarrow100\div x=25\)
\(\Leftrightarrow x=100\div25=4\)
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49 x 37 = 37 x 49
(214 x 25) x 4 = 214 x (25 x 4)
103 x 18 + 103 x 12 = 103 x (18 + 12)
x : 25 : 4 =108
x= 108 x 25 x4
x= 108 x 100
x = 10800
x:25:4=108
x:25=27
x=27/25