Đáp án:
Bài 3:
`a) -2/3 . 4/9 + -2/3 . 5/9 + 1 2/3`
`= -2/3 . (4/9 + 5/9) + 5/3`
`= -2/3 . 1 + 5/3`
`= -2/3 + 5/3`
`= 1`
`b) 3/4 - 2/9 . (-3)^2 + 5/8 : 5`
`= 3/4 - 2/9 . 9 + 5/8 . 1/5`
`= 3/4 - 2 + 1/8`
`= 6/8 - 16/8 + 1/8`
`= -9/8`
Bài 4:
`(2/3 - x) . 2 - 1 3/5 = 2/5`
`(2/3 - x) . 2 - 8/5 = 2/5`
`(2/3 - x) . 2 = 2/5 + 8/5`
`(2/3 - x) . 2 = 2`
`2/3 - x = 2 : 2`
`2/3 - x = 1`
`x = 2/3 - 1`
`x = 2/3 - 3/3`
`x = -1/3`
Vậy `x = -1/3`