Bài 1 (1,5 điểm): Thực hiện phép tính: a) $\frac{4}{9}$ + $\frac{1}{4}$ b) $\frac{1}{3}$.$\frac{-4}{5}$ + $\frac{1}{3}$.$\frac{-1}{5}$ c) $\frac{1}{5}$ - [$\frac{1}{4}$ - (1 - $\frac{1}{2}$)²]

`a) 4/9 + 1/4`

`= 16/36 + 9/36`

`= 25/36`

`1/3.(-4)/5 + 1/3 . (-1)/5`

`= 1/3.(- 4/5 + - 1/5 )`

`= 1/3 . -1`

`= - 1/3`

`1/5 - [ 1/4 - (1 - 1/2 )^2]`

`= 1/5 - [1/4 - 1/2^2 ]`

`= 1/5 - [ 1/4 - 1/4 ]`

`= 1/5 - 0`

`= 1/5`