Giải:
a, `5x - 1/4 = 5/6 - 1/2x`
`-> 5x + 1/2x = 5/6 + 1/4`
`-> (5 + 1/2)x = 10/12 + 3/12`
`-> (10/2 + 1/2)x = 13/12`
`-> 11/2x = 13/12`
`-> x = 13/12 : 11/2`
`-> x = 13/12 . 2/11`
`-> x = 13/66`
Vậy `x = 13/66`
b, `-2/3x + 2/5 = 1/3x - 1/4`
`-> -2/3x - 1/3x = -1/4 - 2/5`
`-> (-2/3 - 1/3)x = -5/20 - 8/20`
`-> -x = -13/20`
`-> x = 13/20`
Vậy `x = 13/20`