Đáp án+Giải thích các bước giải:

Bài `1:`

 `x xx 2/5 -1/2 xx 3/5=10`

`x xx 2/5- 3/10=10`

`x xx 2/5=10+3/10`

`x xx 2/5=\frac{100}{10}+3/10`

`x xx 2/5=\frac{103}{10}`

`x= (103)/(10): 2/5`

`x=\frac{103}{4}`

Vậy `x=\frac{103}{4}`

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`7/20-1/2:x=3/20`

`1/2:x=7/20-3/20`

`1/2:x=4/20`

`1/2:x=1/5`

`x=1/2:1/5`

`x=1/2 xx 5`

`x=5/2`

Vậy `x=5/2`

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`7/9:(x-4/9)=1/2`

`x-4/9=7/9:1/2`

`x-4/9=14/9`

`x=14/9+4/9`

`x=18/9`

`x=2`

Vậy `x=2`

Bài `2:`

`8/x+1/5=2/5+1/3`

`8/x=2/5+1/3-1/5`

`8/x=1/5+1/3`

`8/x=3/15+5/15`

`8/x=8/15`

`x xx 8 =8 xx 15`

`x=\frac{8xx15}{8}`

`x=15`

Vậy `x=15`

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`(1/4+x) xx 2/3=6/7`

`1/4+x=6/7:2/3`

`1/4+x=9/7`

`x=9/7-1/4`

`x=36/28-7/28`

`x=29/28`

Vậy `x=29/28`

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`(x-3/5):1/5=5/8`

`x-3/5=5/8. 1/5`

`x-3/5=1/8`

`x=1/8+3/5`

`x=5/40+24/40`

`x=29/40`

Vậy `x=29/40`