$_@Minz_$
Bài $1:$ Tìm số nguyên $x$ biết:
$a/$ `x/12` $=$ `6/18`
`x/12` $×$ `18/6`
$x = (12.6)÷18$
Vậy $x=9$
$b/$ `8/16` $=$ `4/-x`
`8/16` $×$ `-x/4`
$-x=(16.4)÷8$
Vậy $-x = 8$
Bài $2:$ Thực hiện phép tính:
$a/$ `-4/15` $+$ `-1/15` $=$ `-5/15`
$b/$ `-4/5` $-$ $3$ $=$ `-4/5` $-$ `3/1`
$=$ `-4/5` $-$ `-15/5` $=$ `11/5`
$c/$ `1/4` $-$ `1/3` $+$ `1/12` $=$ `3/12` $-$ `4/12` $+$ `1/12`
$=$ `-1/12` $+$ `1/12` $=$ `0/12`
$d/$ `-4/9` $+$ `3/7` $+$ `5/11` $+$ `5/-9` $+$ `6/11` $=$ $($ `-4/9` $+$ `-5/9` $)+($ `5/11` $+$ `6/11` $)+$ `3/7` $=-1+1+$ `3/7`$=0+$ `3/7` $=$ `3/7`
