bài 5
`a) 4/5 . x = 5/4 - 0,25`
`4/5 . x = 1`
`x = 1 : 4/5`
`x = 5/4`
`b) 3/4 . x + 1/5 = 1/6`
`3/4 . x = 1/6 - 1/5`
`3/4 . x = -1/30`
`x = -1/30 : 3/4`
`x= -2/45`
Bài 6
`a) 7/12 + 5/12 : 6 - 11/6`
`= 7/12 + 5/72 - 11/6`
`= 42/72 + 5/72 - 132/72`
`= -85/72`
`b) ( 4/5 + 1/2) : ( 3/13 - 8/13)`
`= 13/10 : (-5/13)`
`= -169/50`