$\text{1.}$ `3 1/2 - 2 : (5 - 3/4x) = 250%`
`7/2 - 2 : ( 5 - 3/4x) = 5/2`
`2 : ( 5 - 3/4x) = 7/2 - 5/2`
`2 : ( 5 - 3/4x) = 1`
`( 5 - 3/4x) = 2 : 1`
`5 - 3/4x = 2`
`3/4 x = 5 - 2`
`3/4x = 3`
`x = 3 : 3/4`
`x= 4`
$\text{Vậy}$ `x = 4`
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$\text{2.}$ `135 - 5^x = |-10| . (-1)^2020`
`135 - 5^x = 10 . 1`
`135 - 5^x = 10`
`5^x = 135 - 10`
`5^x = 125`
`5^x=5^3`
$\Rightarrow$ `x = 3`
$\text{Vậy}$ `x = 3`
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$\text{3.}$ `75% . (-2)^2 + 4 1/3 - 1/3 : (-1 +1 1/6)`
`= 3/4 . 4 + 13/3 - 1/3 : 1/6`
`= 3 + 13/3 - 2`
`= 22/3 - 2`
`= 16/3`
$\text{Vậy phép tính trên bằng}$ `16/3`
