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Đáp án `+` Giải thích các bước giải`:`

`1.26.`

`a) x + 0,25=1/2`

`x+1/4=1/2`

`x=1/2-1/4`

`x=1/4`

`->` Vậy `x=1/4`

`b) x - (-5/7)=9/14`

`x+5/7=9/14`

`x=9/14-5/7`

`x=-1/14`

`->` Vậy `x=-1/14`

`1/27.`

`a) x - (5/4-7/5)=9/20`

`x-(-3/20)=9/20`

`x+3/20=9/20`

`x=9/20-3/20`

`x=6/20=3/10`

`->` Vậy `x=3/10`

`b) 9-x=8/7-(-7/8)`

`9-x=8/7+7/8`

`9-x=113/56`

`x=9-113/56`

`x=391/56`

`1/28.`

`a) -1,2+(-0,8)+0,25+5,75-2021`

`= -1,2-0,8+(0,25+5,75)-2021`

`= -(1,2+0,8)+6-2021`

`= -2+6-2021`

`= 4-2021`

`= -2017`

`b) -0,1 +16/9+11,1+(-20)/9`

`= (-0,1+11,1) + (16/9+(-20)/9)`

`= 11+-4/9`

`= 95/9`

`1.29`

`a) 17/11 -(6/5-16/11)+26/5`

`= 17/11-6/5+16/11+26/5`

`= (17/11+16/11)+(26/5-6/5)`

`= 33/11+20/5`

`= 3+4`

`= 7`

`b) 39/5 + (9/4-9/5)-(5/4+6/7)`

`= 39/5+9/4-9/5-5/4-6/7``

`= (39/5-9/5)-(9/4-5/4)-6/7`

`= 30/5-4/4-6/7`

`= 6+1-6/7`

`= 7-6/7`

`= 43/7`