Bải 1 (2 điểm) Thực hiện phép tỉnh (tỉnh hợp lý nếu có thể): a) $\frac{-7}{16}$ + $\frac{3}{16}$  b) $\frac{1}{7}$+ $\frac{-9}{27}$ +$\frac{10}{7}$ + $\frac{-4}{7}$  c) $\frac{4}{9}$. $\frac{-7}{26}$ + $\frac{45}{-26}$ .$\frac{4}{9}$ +$\frac{1}{3}$ 

Đáp án + Giải thích các bước giải:

`a)` $\dfrac{-7}{16}$ `+` `3/16`

`=` $\dfrac{(-7)+3}{16}$

`=` $\dfrac{-4}{16}$

`=` $\dfrac{-1}{4}$

`b)` `1/7` `+` $\dfrac{-9}{27}$ `+` `10/7` `+` $\dfrac{-4}{7}$

`=` `(` `1/7` `+` `10/7` `-` `4/7` `)` `-` `1/3`

`=` `(` $\dfrac{1+10-4}{7}$ `)` `-` `1/3`

`=` `7/7` `-` `1/3`

`=` `1` `-` `1/3`

`=` `3/3` `-` `1/3`

`=` `2/3`

`c)` `4/9` `.` $\dfrac{-7}{26}$ `+` `45/-26` `.` `4/9` `+` `1/3`

`=` `4/9` `.` `(` $\dfrac{-7}{26}$ `-` `45/26` `)` `+` `1/3`

`=` `4/9` `.` `(` $\dfrac{(-7)-45}{26}$ `)` `+` `1/3`

`=` `4/9` `.` $\dfrac{-52}{26}$ `+` `1/3`

`=` `4/9` `.` `(` `-2` `)` `+` `1/3`

`=` $\dfrac{-8}{9}$ `+` `1/3`

`=` $\dfrac{-8}{9}$ `+` `3/9`

`=` $\dfrac{-5}{9}$

           `- - -~kid20~- - -`