Câu 16 (1,5 điểm) Thực hiện phép tính a) $\frac{1}{7}$: $\frac{-6}{21}$  b) $-2\frac{1}{2}$: $\frac{10}{7}$ -25% c)  $\frac{3}{11}$. $\frac{5}{9}$ + $\frac{12}{11}$.$\frac{5}{9}$ -$\frac{5}{9}$. $\frac{4}{11}$ 

`16 . `

`a . ` `1/7:(-6)/21`

`=` `1/7*21/(-6)`

`=` `-1/2`

$\\$

`b . ` `-2 1/2:10/7-25%`

`=` `-5/2:10/7-1/4`

`=` `-5/2*7/10-1/4`

`=` `-(5*7)/(2*10)-1/4`

`=` `-7/4-1/4`

`=` `-2`

$\\$

`c . ` `3/11*5/9+12/11*5/9-5/9*4/11`

`=` `5/9*(3/11+12/11-4/11)`

`=` `5/9*1`

`=` `5/9`

`#me`