Bài 1 :

`a, (\frac{1}{2} + \frac{3}{5}) : \frac{11}{5}`

`= \frac{5 + 6}{10} : \frac{11}{5}` 

`= \frac{11}{10} xx \frac{5}{11}`

`= \frac{5}{10} = 1/2`

`b, 2,9 + 3,7 + (-4,2) + (-2,9) + 4,2`

`= (-2,9 + 2,9) + (-4,2 + 4,2) + 3,7`

`= 0 + 0 + 3,7 = 3,7`

Bài 2 :

`a, \frac{x}{12} = \frac{2}{4}`

`=> 4x = 12 . 2`

`=> 4x = 24`

`=> x = 24 : 4`

`=> x = 6`

Vậy `x = 6`

`b, ( x - 2)^3 = 8`

`=> (x-2)^3 = 2^3`

`=> x - 2 = 2`

`=> x = 2 + 2`

`=> x = 4`

Vậy `x = 4`

$#Gửi tuss hieunguyen9002 $

`a, `

`( 1/2 + 3/5 ) : 11/5 `

`= 11/10 : 11/5` 

`= 11/10 . 5/11`

`= 1/2`

`b, `

`2,9 + 3,7 + ( - 4,2 ) + ( -2,9 ) +4,2` 

`= 3,7 + 2,9 + ( -2,9 ) + ( - 4,2 ) + 4,2  `

`= 3,7 + 0 + 0` 

`= 3,7` 

_____________________________________________________________

`a,` 

`x/12 = 2/4 `

`x : 12 = 0,5` 

      ` x = 0,5 . 12 `

       `x = 6 `

`b.` 

`( x - 2 )^3 = 8 `

`( x - 2 )^3 = 2 ^3` 

              `x = 2 + 2` 

              `x = 4 `