Bài 1 :

`25% - 28/13 - (-1/2) ^2 + 0,25 : 1/25`

`= 1/4 - 28/3 - 1/4 + 1/4 : 1/25`

`= 1/4 - 28/3 - 1/4 + 25/4`

`= (1/4 - 1/4) - 28/3 + 25/4`

`= 0 - 28/3 + 25/4`

`= -112/52 + 325/52 =213/52`

`=> 213/52≈4,096`

   `( 4,5 - 4/7.x ) : 5/6 = 0,6`     

` 4/5 - 4/7.x = 0, 6 . 5/6`

`4/5 - 4/7.x = 1/2`

`4/7.x          = 4/5 - 1/2`

` 4/7.x         = 3/10`

`x                =3/10 : 4/7`

`x                = 21/40`

`=> x = 21/40`

`color{pink}{text} T h o 216`