Đáp án:
`a, 5/8 + 2x = 3/10`
`2x = 3/10 - 5/8 = 12/40 - 25/40`
`2x = -13/40`
`x = -13/40 : 2 = -13/40 . 1/2`
`x = -13/80`
`b, 7/9 : (2 + 3/4 x) + 5/9 = 23/27`
`⇔ 7/9 : (2+ 3/4 x) = 23/27 - 5/9 = 23/27 - 15/17`
`⇔ 7/9 : (2 + 3/4 x) = 8/27`
`⇔ 2 + 3/4 x = 7/9 : 8/27 = 7/9 . 27/8`
`⇔ 2 + 3/4 x = 21/8`
`⇔ 3/4 x = 21/8 - 2`
`⇔ 3/4 x = 5/8`
`⇔ x = 5/8 : 3/4 = 5/8 . 4/3`
`⇒ x = 5/6`
`c, (2,4 x - 3) : 1 5/7 = - 1`
`⇔ (2,4 x - 3) : 12/7 = -1`
`⇔ 2,4 x - 3 = - 1 . 12/7`
`⇔ 2,4 x - 3 = -12/7`
`⇔ 2,4 x = -12/7 + 3`
`⇔ 2,4 x = 9/7`
`⇔ x = 9/7 : 2,4`
`⇒ x = 15/28`
`d, 2/5 - (25%x + 1) = 1 2/5`
`⇔ 2/5 - (25/100 x + 1) = 7/5`
`⇔ 1/4 x + 1 = 2/5 - 7/5`
`⇔ 1/4 x + 1 = - 5/5 = -1`
`⇔ 1/4 x = - 1 - 1`
`⇔ 1/4 x = -2`
`⇔ x = -2 : 1/4 = -2. 4/1`
`⇔ x = - 8`
`e, 15% x - 2,3 x = 43/45`
`⇔ 15/100 x - 23/10 x = 43/45`
`⇔ 3/20 x - 46/20 x = 43/45`
`⇔ -43/20 x = 43/45`
`⇔ x = 43/45 : (-43)/20 = 43/45 . 20/-43`
`⇒ x = -4/9`
`f, 1/3 (2x - 1) + 2/5 = 3(x - 1/5) - 7/10`
`⇔ 1/3 . 2x - 1/3 .1 + 2/5 = 3.x - 3.1/5 -7/10`
`⇔ 2/3 x - 1/3 + 2/5 = 3x - 3/5 - 7/10`
`⇔ 2/3 x - 3x = -3/5 - 7/10 + 1/3 - 2/5`
`⇔ 2/3 x - 9/3 x = -18/30 - 21/30 + 10/30 - 12/30`
`⇔ -7/3 x = - 41/30`
`⇔ x = -41/30 : (-7)/3 = -41/30 . 3/(-7)`
`⇔ x = 41/70`
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