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Bài `4`

`a) ( 3/15 - x ) . 1/3 = 2/5`

`3/15 - x = 2/5 : 1/3`

`3/15 - x = 2/5 . 3`

`3/15 - x = 6/5`

`x = 3/15 - 6/5`

`x = -15/15 = -1`

Vậy `x = -1`

`b) 3/5 . x - 1/3 = 1/4`

`3/5 . x = 1/4 + 1/3`

`3/5 . x = 3/12 + 4/12`

`3/5 . x = 7/12`

`x = 7/12 : 3/5`

`x = 7/12 . 5/3`

`x = 35/36`

Vậy `x = 35/36`

`c) 1/4 + 3/4 : x = -2`

`3/4 : x = -2 - 1/4`

`3/4 : x = -8/4 - 1/4`

`3/4 : x = -9/4`

`x = 3/4 : ( -9/4 )`

`x = 3/4 . 4/-9`

`x = 1/-3`

Vậy `x = 1/-3`

`d) 3/4 + 2 ( 2x - 2/3 ) = 2`

`2 . ( 2x - 2/3 ) = 2 - 3/4`

`2 . ( 2x - 2/3 ) = 8/4 - 3/4`

`2 . ( 2x - 2/3 ) = 5/4`

`2x - 2/3 = 5/4 : 2`

`2x - 2/3 = 5/4 . 1/2`

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

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

`2x = 15/24 + 16/24`

`2x = 31/24`

`x = 31/24 : 2`

`x = 31/24 . 1/2`

`x = 31/48`

Vậy `x = 31/48`

`e) 2 . ( 1/2 x - 1/3 ) - 3/2 = 1/4`

`2 . ( 1/2 x - 1/3 ) = 1/4 + 3/2`

`2 . ( 1/2 x - 1/3 ) = 1/4 + 6/4`

`2 . ( 1/2 x - 1/3 ) = 7/4`

`1/2 x - 1/3 = 7/4 : 2`

`1/2 x - 1/3 = 7/4 . 1/2`

`1/2 x - 1/3 = 7/8`

`1/2 x = 7/8 + 1/3`

`1/2 x = 21/24 + 8/24`

`1/2 x = 29/24`

`x = 29/24 : 1/2`

`x = 29/24 . 2`

`x = 29/12`

Vậy `x = 29/12`

`#T`