Gợi ý bừa thôi : bạn dùng máy tính casio ( ko có thì thôi )
`(13/39-45/268) - ( -2/3 + 0,5 . 40% - 45/268)`
`=13/39-45/268 - 2/3- 1/2 . 2/5 + 45/268`
`= 13/39+(-45/268+ 45/268) - 2/3- 1/2 . 2/5`
`= 13/39- 2/3- 1/2 . 2/5`
`= 13/39- 2/3- 1/5`
`= 13/39- 26/39 - 1/5`
`= -1/3 -1/5`
`= -5/15 -3/15`
`= -8/15`