Bài 1: (2 điểm) Thực hiện phép tính (tính nhanh nếu có thể): a) $\frac{1}{5}$+ $\frac{-5}{19}$+ $\frac{4}{5}$+ $\frac{-4}{19}$  b) $\frac{1}{5}$. $\frac{11}{16}$+ $\frac{1}{5}$. $\frac{5}{16}$+ $\frac{4}{5}$  c) 25% $- 1\frac{1}{2}$+ $0,5\frac{3}{8}$  d) $(\frac{-1}{6})^2$: $\frac{5}{-24}$+ $(\frac{7}{25}$- 36%) .$|-8\frac{1}{2}|$ 

Đáp án:

 `a)10/19`

`b)1`

`c)-17/16`

`d)-4/5`

Giải thích các bước giải:

 `a)`

`1/5+\frac{-5}{19}+4/5+\frac{-4}{19}`

`=(1/5+4/5)-(5/19+4/19)`

`=5/5-9/19`

`=1-9/19`

`=19/19-9/19`

`=10/19`

`b)`

`1/5 . 11/16+ 1/5 . 5/16+4/5`

`=1/5 . (11/16+5/16)+4/5`

`=1/5. 16/16+4/5`

`=1/5. 1+4/5`

`=1/5+4/5`

`=5/5`

`=1`

`c)`

`25%-1 1/2+0,5. 3/8`

`=25/100- 3/2+ 5/10. 3/8`

`=1/4-3/2+1/2. 3/8`

`=1/4-3/2+3/16`

`=4/16-24/16+3/16`

`=-17/16`

`d)`

`(\frac{-1}{6})^{2}: 5/-24+(7/25-36%).|-8 1/3|`

`=1/36: (-5/24)+(7/25-36/100). 8 1/3`

`=1/36. (-24/5)+(7/25-9/25). 25/3`

`=-2/15+(-2/25). 25/3`

`=-2/15-2/3`

`=-2/15-10/15`

`=-12/15`

`=-4/5`