Đáp án:

Giải thích các bước giải:

Bài 1:

`a)`

`1/8 + 3/8 = 4/8 = 1/2`

`b)`

`(-1)/2 + (-5)/3 = (-3)/6 + (-10)/6 = (-13)/6`

`c)`

`(-6)/35 . (-49)/54 = (-6)/(5 . 7) . (-7 . 7)/(6 . 9) = 7/45`

`d)`

`(-4)/5 : 3/4 = (-4)/5 . 4/3 = (-16)/15`

`e)`

`31/17 + (-5)/13 + (-8)/13 - 14/17`

`= (31/17 - 14/17) + ((-5)/13 + (-8)/13)`

`= 17/17 + (-13)/13`

`= 1 + -1`

`= 0`

`f)`

`5/7 . 2/11 + 5/7 . 9/11 + (-5)/7`

`= 5/7 . (2/11 + 9/11) + (-5)/7`

`= 5/7 . 11/11 + (-5)/7`

`= 5/7 . 1 + (-5)/7`

`= 5/7 + (-5)/7`

`= 0`

Bài 2:

`a)`

`( 2 4/5x - 50 ) : 2/3 = 51`

`<=> 14/5x - 50 = 34`

`<=> 14/5x = 84`

`=> x = 84 : 14/5`

`=> x = 84 . 5/14`

`=> x = 6 . 5`

`=> x = 30`

`b)`

`12 - x = 4(2x - 3) + 2`

`<=> 12 - x - 4 (2x - 3) - 2 = 0`

`<=> 12 - x - 8x + 12 - 2 = 0`

`<=> -9x = -22`

`<=> x = 22/9`

 Đáp án+Giải thích các bước giải:

 `text{Bài 1:}`

`a) 1/8+3/8`

`=(1+3)/8`

`=4/8`

`=1/2`

 `b) -1/2+(-5)/3`

`=-3/6-10/6`

`=-13/6`

 `c) (-6)/35*(-49)/54`

`=(-6)/(5*7)*(-7*7)/(6*9)`

`=7/45`

 `d) -4/5÷3/4`

`=-4/5*4/3`

`=-16/15`

 `e) 31/17+(-5)/13+(-8)/13-14/17)`

`=(31/17-14/17)-(5/13+8/13)`

`=17/17-13/13`

`=1-1`

`=0`

 `f) 5/7*2/11+5/7*9/11+(-5)/7`

`=5/7(2/11+9/11)-5/7`

`=5/7*1-5/7`

`=5/7-5/7`

`=0`

`text{Bài 2:}`

 `a) (2(4)/5x-50)÷2/3=51`

`<=>14/5x-50=51*2/3`

`<=>14/5x-50=34`

`<=>14/5x=34+50`

`<=>14/5x=84`

`<=>x=84÷14/5`

`<=>x=30`

 `b) 12-x=4(2x-3)+2`

`<=>12-x=8x-12+2`

`<=>9x=12+12-2`

`<=>9x=22`

`<=>x=22/9`