Đáp án:

 `1)`

`-(251xx3+281)+3xx251-(1-281)`

`=-251xx3-281+3xx251-1+281`

`=3xx(251-251)+(281-281)-1`

`=3xx0+0-1`

`=-1`

`2)`

`[2,5xx0,38.(-0,4)]-[-0,125xx3,15xx8]`

`=[(2,5xx(-0,4))xx0,38]-[(-0,125xx8)xx3,15]`

`=(-1)xx0,38-(-1)xx3,15`

`=-0,38+3,15`

`=2,77`

`3)`

`[(-20,83)xx0,2+(-9,17)xx0,2+(-9,17)xx0,2]:[2,47xx0,5-(-3,53)xx0,5]`

`=[0,2xx(-20,83-9,17-9,17)]:[0,5xx(2,47-(-3,53)]`

`=[0,2xx(-39,17)]:[0,5xx6]`

`=(-7,834):3`

`=-(3917)/(1500)`

_______________________________________________________

(bỏ một `-9,17xx0,2`)

`[(-20,83)xx0,2+(-9,17)xx0,2]:[2,47xx0,5-(-3,53)xx0,5]`

`=[0,2xx(-20,83-9,17)]:[0,5xx(2,47-(-3,53)]`

`=[0,2xx(-30)]:[0,5xx6]`

`=(-6):3`

`=-2`

`4)`

`-12,7xx32,6+2,7xx12,8+12,7xx2,6+2,7xx17,2`

`=12,7xx(-32,6+2,6)+2,7xx(12,8+17,2)`

`=12,7xx(-30)+2,7xx30`

`=30xx(-12,7+2,7)`

`=30xx(-10)`

`=-300`

1)-(251 3+ 281)+3×251-(1-281)

=-251-281+3×251-1+281

=(-251×3+3×251)+(-281+281)-1

=0+0-1

=-1

3)

[ ( - 20,83 ) . 0,2 + ( -9,17 ) . 0,2 ] : [ 2,47 . 0,5 - ( -3,53 ) - 0,5 ]

= { 0,2 . [( - 20,83) + (-9,17) } : [ 2,47 . 0,5 + 3,53 - 0,5 ]

= { 0,2 .  (-30) } : [ 2,47 . 0,5 - 0,5 + 3,53 ]

= -6 : [ 0,5 . (2,47-1 ) + 3,53 ]

= -6 : [ 0,5 . 1,47+ 3,53 ]

= -6 : [ 0,735 + 3,53 ]

= -6 : 4,265

= -1200/853

4)12,7.(−32,6)+2,7.12,8+12,7.2,6+2,7.17,2

=12,7(−32,6+2,6)+2,7(12,8+17,2)A

=12,7.(−30)+2,7.30

=30(−12,7+2,7)

=30.(−10)

=−300