Đáp án:
`a) x =` `7/20`
`b) x =` `31/15`
`c) x =` `3/10`
`d) x =` `8/3`
`e) x =` `(-17)/6`
`f) x =` `(-13)/20`
Giải thích các bước giải:
Bài `3 :`
`a) x +` `1/4` `=` `3/5`
`=> x =` `3/5` `-` `1/4`
`=> x =` `12/20` `-` `5/20`
`=> x =` `7/20`
Vậy `x =` `7/20`
`b) x -` `2/5` `=` `5/3`
`=> x =` `5/3` `+` `2/5`
`=> x =` `25/15` `+` `6/15`
`=> x =` `31/15`
Vậy `x =` `31/15`
`c)` `1/2` `- x =` `1/5`
`=> x =` `1/2` `-` `1/5`
`=> x =` `5/10` `-` `2/10`
`=> x =` `3/10`
Vậy `x =` `3/10`
`d)` `1/4` `. x +` `5/3` `=` `7/3`
`=>` `1/4` `. x =` `7/3` `-` `5/3`
`=>` `1/4` `. x =` `2/3`
`=> x =` `2/3` `:` `1/4`
`=> x =` `2/3` `. 4`
`=> x =` `8/3`
Vậy `x =` `8/3`
`e)` `(-3)/2` `. x -` `7/2` `=` `3/4`
`=>` `(-3)/2` `. x =` `3/4` `+` `7/2`
`=>` `(-3)/2` `. x =` `3/4` `+` `14/4`
`=>` `(-3)/2` .` x =` `17/4`
`=> x =` `17/4` : `(-3)/2`
`=> x =` `17/4` . `(-2)/3`
`=> x =` `(-17)/6`
Vậy `x =` `(-17)/6`
`f)` `(-1)/4` `- x =` `2/5`
`=> x =` `(-1)/4` `-` `2/5`
`=> x =` `(-5)/20` - `8/20`
`=> x =` `(-13)/20`
Vậy `x =` `(-13)/20`
