Đáp án `+` Giải thích các bước giải:

1) `(x + 1/2) . 2/5 = 7/5`

`x + 1/2 = 7/5 : 2/5`

`x + 1/2 = 7/5 . 5/2`

`x + 1/2 = 7/2`

`x = 7/2 - 1/2`

`x = 6/2`

`x = 3.`

2) `(7/2 - x) : 4/5 = -21/20`

`7/2 - x = -21/20 . 4/5`

`7/2 - x = -21/25`

`x = 7/2 - (-21)/25`

`x = 105/50 + 42/50`

`x = 147/50.`

3) `3 - (1/6 - x) . 2/3 = 2/3`

`3 - (1/6 - x) = 2/3 : 2/3`

`3 - (1/6 - x) = 2/3 . 3/2`

`3 - (1/6 - x) = 1`

`1/6 - x = 3 - 1`

`1/6 - x = 2`

`x = 1/6 - 2`

`x = -11/6.`

4) `(x - 5/8) . 5/18 = -15/36`

`(x - 5/8) . 5/18 = -5/12`

`x - 5/8 = -5/12 : 5/18`

`x - 5/8 = -5/12 . 18/5`

`x - 5/8 = -3/2`

`x = -3/2 + 5/8`

`x = -12/8 + 5/8`

`x = -7/8.`

5) `(x - 5/2) . 10/3 = 22/3`

`x - 5/2 = 22/3 : 10/3`

`x - 5/2 = 22/3 . 3/10`

`x - 5/2 = 11/5`

`x = 11/5 + 5/2`

`x = 22/10 + 25/10`

`x = 47/10.`

6) `21/4 . (x - 71/3) = 3/2`

`x - 71/3 = 3/2 : 21/4`

`x - 71/3 = 3/2 . 4/21`

`x - 71/3 = 2/7`

`x = 2/7 + 21/3`

`x = 6/21 + 147/21`

`x = 151/21.`

7) `(x + 5/6) : 5/12 - 5/4 = 7/20`

`(x + 5/6) : 5/12 = 7/20 + 5/4`

`(x + 5/6) : 5/12 = 7/20 + 25/20`

`(x + 5/6) : 5/12 = 32/20`

`(x + 5/6) : 5/12 = 8/5`

`x + 5/6 = 8/5 . 5/12`

`x + 5/6 = 2/3`

`x = 2/3 - 5/6`

`x = 4/6 - 5/6`

`x = -1/6.`

8) `27/9 - 3/4 . (x + 1) = 7/9`

`3/4 . (x + 1) = 27/9 - 7/9 `

`3/4 . (x + 1) = 20/9`

`x + 1 = 20/9 : 3/4`

`x + 1 = 20/9 . 4/3`

`x + 1 = 5/3`

`x = 5/3 - 1`

`x = 2/3.`

9) `(24/5x - 50) : 2/3 = 51`

`24/5x - 50 = 51 . 2/3`

`24/5x - 50 = 34`

`24/5x = 34 + 50`

`24/5x = 84`

`x = 84 : 24/5`

`x = 84 . 5/24`

`x = 7 . 5/2`

`x = 35/2.`

10) `1/2 + 3/5 . (x - 2) = 1/5`

`3/5 . (x - 2) = 1/5 - 1/2`

`3/5 . (x - 2) = 2/10 - 5/10`

`3/5 . (x - 2) = -3/10`

`x - 2 = -3/10 : 3/5`

`x - 2 = -3/10 . 5/3`

`x - 2 = -1/2`

`x = -1/2 + 2`

`x = 3/2.`

11) `4/5 + 5/7 : x = 1/6`

`5/7 : x = 1/6 - 4/5`

`5/7 : x = 5/30 - 24/30`

`5/7 : x = -19/30`

`x = 5/7 : (-19)/30`

`x = 5/7 . (-30)/19`

`x = -150/133.`

12) `4/7x - 2/3 = 1/5`

`4/7x = 1/5 + 2/3`

`4/7x = 3/15 + 10/15`

`4/7x = 13/15`

`x = 13/15 : 4/7`

`x = 13/15 . 7/4`

`x = 91/60.`