Câu `1:`
`a) 3/4 + 7/3 - 1/2`
`= 9/12 + 28/12 - 6/12`
` = (9+28-6)/12`
` = 31/12`
`b) (-3)/5 . 11/6 + 4/6 . (-3)/5`
` = (-3)/5 . (11/6 + 4/6)`
` = (-3)/5 . 5/2`
` = -3/2`
`c) 0,8 : (25% - 2 1/4) + 4/5`
` = 4/5 : ( 1/4 - 9/4) +4/5`
` = 4/5 : (-2) + 4/5`
` = -2/5 + 4/5`
` = 2/5`
Câu `2:`
`a) (-1)/5 + x = 9/5`
`=> x = 9/5 - (-1)/5`
`=> x = 2`
Vậy `x=2`
`b) 4/5 + 1/5.(x+1/2) = -2/3`
`=> 1/5 . (x+1/2) = -2/3 - 4/5`
`=> 1/5 . (x+1/2) = -22/15`
`=> x+1/2 = -22/15 : 1/5`
`=> x+1/2 = -22/3`
`=> x = -22/3 - 1/2`
`=> x = -47/6`
Vậy ` x=-47/6`
`c) |2/3x-1/4| - 1 = 0,5`
` => |2/3x-1/4| = 0,5 + 1`
`=> |2/3x-1/4| = 3/2`
`=> 2/3x-1/4 = 3/2` hoặc `2/3x - 1/4 = (-3)/2`
`+) 2/3x - 1/4 = 3/2`
`=> 2/3x = 7/4`
`=> x = 21/8`
`+) 2/3x - 1/4 = (-3)/2`
`=> 2/3x = -5/4`
`=> x = -15/8`
Vậy `x \in{21/8 ; (-15)/8}`
