Bài 1(2.5 điểm) Tính giá trị các biểu thức sau: a) $\frac{-3}{8}$ + $\frac{5}{12}$  b) $\frac{-5}{7}$. $\frac{2}{11}$+ $\frac{-5}{7}$. $\frac{9}{11}$+ $\frac{5}{7}$  c) $\frac{2}{-11}$. $6\frac{2}{7}$+ $\frac{4}{7}: 4 -2 $ d)$ 1,75 : 5 + 2,5 . ( 4^2-4. 4,1)$

Đáp án`+`Giải thích các bước giải :

`a)``-3/8+5/12`

`=-9/24+10/24`

`=1/24`

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`b)``(-5)/7 . 2/11+(-5)/7 . 9/11+5/7`

`=-5/7 . (2/11+9/11-1)`

`=-5/7 . 0`

`=0`

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`c)``2/(-11) . 6 2/7 + 4/7:4-2`

`=-2/11 . 44/7+4/7 . 1/4-2`

`=-8/7+1/7-2`

`=-7/7-2`

`=-1-2`

`=-3`

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`d)``1,75:5+2,5.(4^2-4.4,1)`

`=0,35+2,5.(16-16,4)`

`=0,35+2,5.(-0,4)`

`=0,35-1`

`=-0,65`