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a, 70 - 5 ( x - 3 ) = 45
⇔ 5 . x - 3 = 70 - 45
⇔ 5 x - 3 = 35
⇔ x - 3 = 35 : 5 ⇔ x - 3 = 7
⇔ x = 10
b, 10 + 2 x = 4 5 : 4 3
⇔ 10 + 2 x = 4 2 ⇔ 10 + 2 x = 16
⇔ 2 x = 4 ⇔ x = 2
c, 60 - 3 x - 2 = 51
⇔ 3 x - 2 = 60 - 51
⇔ 3 x - 2 = 9
⇔ x - 2 = 3 ⇔ x = 5
d, 4 x - 20 = 2 5 : 2 3
⇔ 4 x - 20 = 2 2 ⇔ 4 x - 20 = 4
⇔ 4 x = 24 ⇔ x = 6
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[ 45+ (52 -20 ) ] .x =103 .15
=> (45+5).x=1000.15
=> 50x=15000
=> x=15000:50
=> x=300
[ 45 + (52 -20 ) ] .x =103 .15
(45 + 5) . x = 15000
50 . x = 15000
x = 15000 : 50
x = 300
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A, 7[x + 5] - 20 = 190
7x + 35 - 20 = 190
7x + 15 = 190
7x = 175
x = 25
B, 155 - 10[x + 1] = 55
155 - 10x - 10 = 55
-10x + 90 = 55
-10x = -35
x = 3.5
C, 6[x + 2^3] + 40 = 100
6[x + 8] + 40 = 100
6x + 48 + 40 = 100
6x + 88 = 100
6x = 1
2 x = 2
D, 15x - 133 = 17
15x = 150
x = 10
E, 90[x + 2] = 45
90x + 180 = 45
90x = -135
x = -1.5
F, 4x + 54 = 82
4x = 28
x = 7
G, 17x - 20 = 14
17x = 34
x = 2
\(\dfrac{20}{45}-\left(\dfrac{2}{3}-10\right)=\dfrac{4}{9}-\left(\dfrac{2-30}{3}\right)=\dfrac{4}{9}-\left(-\dfrac{28}{3}\right)=\dfrac{4}{9}+\dfrac{28}{3}=\dfrac{4}{9}+\dfrac{84}{9}=\dfrac{88}{9}\)
20/45-(2/3-10)
=20/45-(2/3-10/1)
=20/45-28/3=167/135