Bài `1`:
`a) 0,4x - 1/4x = 12/18 + (-11)/12`
`=> 0,4x - 0,25x = 2/3 - 11/12`
`=> x. (0,4 - 0,25) = 8/12 - 11/12`
`=> x. 0,15 = -1/4`
`=> x = -1/4 : 0,15`
`=> x = -5/3`
Vậy `x = -5/3`
`b) ( (3x)/4 + 10) : (-12) = (-16)/51 : 8/17`
`=> 3/4 x + 10 = -16/51. 17/8. (-12)`
`=> 3/4 x + 10 = 8`
`=> 3/4x = 8 - 10`
`=> 3/4x = -2`
`=> x = -2 : 3/4`
`=> x = -8/3`
Vậy `x = -8/3`
Bài `2`:
`a) (-9)/34. 61/63 + 2/63. (-9)/34 + 2/17`
`= (-9)/34. (61/63 + 2/63) + 2/17`
`= (-9)/34. 1 + 2/17`
`= (-9)/34 + 4/34`
`= -5/34`
`b) (85 7/25 + 13 2/47) - 81 7/25`
`= (85 7/25 - 81 7/25) + 13 2/47`
`= 4 + 13 2/47`
`= 17 2/47`
`= 801/47`
`c) 4/5. 3/8 + 4/8. 3/11 + ... + 4/95. 3/98 + 4/98. 3/101`
`= 4. 3/(5.8) + 4. 3/(8.11) + ... + 4. 3/(95.98) + 4. 3/(98.101)`
`= 4. ( 3/(5.8) + 3/(8.11) + ... + 3/(95.98) + 3/(98.101))`
`= 4. (1/5 - 1/8 + 1/8 - 1/11 + ... + 1/95 - 1/98 + 1/98 - 1/101)`
`= 4. (1/5 - 1/101)`
`= 4. 96/505`
`= 384/505`
