Bài $1$.
$1$. `1/5 + x = {-2}/3`
`x = {-2}/{3} - 1/5`
`x = {-13}/{15}`
Vậy `x = {-13}/{15}`
$2$. `{-5}/8 + x = 4/9`
`x = 4/9 - {-5}/{8}`
`x = 4/9 + 5/8`
`x = {77}/{72}`
Vậy `x = {77}/{72}`
$3$. `1{3}/{4} x +1 {1}/{2} = {-4}/5`
`{7x}/{4} + 3/2 = {-4}/5`
`{7x}/{4} = \frac{-23}{10}`
`70x = -92$
` x = \frac{-46}{35}`
Vậy ` x = \frac{-46}{35}`
$4$. `x. ( 1/5 + 1/5 ) - (1/7 +1/8 ) =0`
`x . 2/5 = \frac{15}{56}`
`x = \frac{75}{112}`
Vậy `x = \frac{75}{112}`
Bài $2$.
$1$. `7,5 . {-2}/5 . 2,5`
`= \frac{15}{2} . {-2}/5 . \frac{5}{2}`
`= \frac{15.(-2).5}{2.5.2}`
`= \frac{-15}{2}`
$2$. `-50,5 . 8 . (-0,25)`
`=\frac{-101}{2} . 8 . \frac{-1}{4}`
`= \frac{-101.8.(-1)}{2.4}`
`= \frac{-101.(-1)}{1}`
`= 101`
$3$. `0,125 . (-3,7) . (-2)^3`
`= 1/8 . {-37}/{10} . (-8)`
`= \frac{1.(-37).(-8)}{8.10.1}`
`= \frac{-37.(-1)}{10}`
`= \frac{37}{10}`
