17) ($\frac{1}{3}$ + $\frac{12}{67}$ + $\frac{13}{41}$) - ($\frac{79}{67}$ - $\frac{28}{41}$)

= $\frac{1}{3}$ + $\frac{12}{67}$ + $\frac{13}{41}$ - $\frac{79}{67}$ + $\frac{28}{41}$

= $\frac{1}{3}$ + ($\frac{12}{67}$ - $\frac{79}{67}$)+($\frac{13}{41}$ + $\frac{28}{41}$)

= $\frac{1}{3}$ + $\frac{-67}{67}$ + $\frac{41}{41}$

= $\frac{1}{3}$ + (-1) + 1

= $\frac{1}{3}$ 

 18) $\frac{38}{45}$ - ($\frac{8}{45}$ - $\frac{17}{51}$ - $\frac{3}{11}$)

= $\frac{38}{45}$ - $\frac{8}{45}$ + $\frac{17}{51}$ + $\frac{3}{11}$

= $\frac{2}{3}$ + $\frac{17}{51}$ + $\frac{3}{11}$

= $\frac{34}{51}$ + $\frac{17}{51}$ + $\frac{3}{11}$ = 1 + $\frac{3}{11}$

= $\frac{11}{11}$ + $\frac{3}{11}$ = $\frac{14}{11}$ = 1$\frac{3}{11}$ 

19) $\frac{7}{12}$ . $\frac{6}{11}$ + $\frac{7}{12}$ . $\frac{5}{11}$ - 2$\frac{7}{12}$

= $\frac{7}{12}$ . ($\frac{6}{11}$+$\frac{5}{11}$) - $\frac{31}{12}$

= $\frac{7}{12}$ . 1 - $\frac{31}{12}$ = -2

xin hay nhất đấy làm ơn <3

`17) ( 1/3 + 12/67 + 13/41 ) - ( 79/67 - 28/41 )`

`= 1/3 + 12/67 + 13/41 - 79/67 + 28/41`

`= 1/3 - ( 79/67 - 12/67 ) + ( 13/41 + 28/41 )`

`= 1/3 - 67/67 + 41/41`

`= 1/3 - 1 + 1`

`= 1/3 - 0`

`= 1/3`

`18) 38/45 - ( 8/45 - 17/51 - 3/11 )`

 `= 38/45 - 8/45 + 17/51 + 3/11`

`= 30/45 + 1/3 + 3/11`

`= 2/3 + 1/3 + 3/11`

`= 1 + 3/11`

`= 1 3/11 `

`= 14/11`

`19) 7/12. 6/11 + 7/12. 5/11 - 2 7/12`

`= 7/12. ( 6/11 + 5/11 ) - 31/12`

`= 7/12. 1 - 31/12`

`= 7/12 - 31/12`

`= ( -24 )/12`

`= -2`

$\text{#lknhatminh0322}$