Lời giải:

`a, x + (-7)/15 = -1 1/20`

  `x + (-7)/15 = (-21)/20`

  `x = (-21)/20 - (-7)/15`

  `x = (-63)/60 + 28/60`

  `x = (-35)/60`

Vậy `x = (-35)/60`

`b, (3 1/2 - x) * 1 1/4 = -1 1/20`

  `(7/2 - x) * 5/4 = (-21)/20`

  `7/2 - x = (-21)/20 : 5/4`

  `7/2 - x = (-21)/20 * 4/5`

  `7/2 - x = (-21)/5 * 1/5`

  `7/2 - x = (-21)/25`

  `x = 7/2 - (-21)/25`

  `x = 7/2 + 21/25`  

  `x = 175/50 + 42/50`

  `x = 217/50`

Vậy `x = 217/50`

`c, 1/2x + 3/5 * (x - 2) = 3`

  `1/2x + 3/5x - 6/5 = 3`

  `1/2x + 3/5x = 3 + 6/5`

  `5/10x + 6/10x = 15/5 + 6/5`

  `11/10x = 21/5`

  `x = 21/5 : 11/10`

  `x = 21/5 * 10/11`

  `x = 21 * 2/11`

  `x = 42/11`

Vậy `x = 42/11`

`d, 11/12x + 3/4 = (-1)/6`

  `11/12x = (-1)/6 - 3/4`

  `11/12x = (-2)/12 + (-9)/12`

  `11/12x = (-11)/12`

  `x = (-11)/12 : 11/12`

  `x = -1`

Vậy `x = -1`

`e, 3 - (1/6 - x) * 2/3 = 2/3`

  `3 - (1/6 - x) = 2/3 : 2/3`

  `3 - (1/6 - x) = 1`

  `1/6 - x = 3 - 1`

  `1/6 - x = 2`

  `x = 1/6 - 2`

  `x = 1/6 - 12/6`

  `x = (-11)/6`

Vậy `x = (-11)/6`

`f, 8x - 4x = 1208`

 `4x = 1208`

 `x = 1208 : 4`

 `x = 302`

Vậy `x = 302`

Đáp án:

 $f) 8x-4x=1208$

$⇒ 4x=1208$

$⇒ x= 1208:4$

$⇒ x= 302$