Đáp án:
`13, (-7)/15 : (2/5 - 5/9)`
`=(-7)/15 : (-7/45)`
`= 3`
`14, 5 2/3 - (3 1/9 + 1 2/3)`
`= 5 2/3 - 3 1/9 - 1 2/3`
`= (5 2/3 - 1 2/3) - 3 1/9`
`= 4 - 28/9`
`= 8/9`
`15) 19 5/8 : 7/12 - 15 1/4 : 7/12`
`= 157/8 . 12/7 - 61/4 . 12/7`
`= 12/7 . (157/8 - 61/4)`
`= 12/7 . 35/8`
`= 15/2`
`18) 4 3/5 + 1 2/5`
`= 23/5 + 7/5`
`= 6`
`19) (-1/2)^2 : 1/4 - 2 . (-1/2)^3`
`= 1/4 . 4 - 2 . (-1/8)`
`= 1 - (-1/4)`
`= 5/4`
`20) (4 4/5 - 3 3/10) : (-3)`
`= (24/5 - 33/10) : (-3)`
`= 3/2 : (-3)`
`= -1/2`