bài 1)
`a) \frac{-5}{8} . ( 4/9 + \frac{-7}{12})`
`=\frac{-5}{8} . (-5/36)`
`= 25/288`
`b) (-3,2) . \frac{-15}{64} + ( 0,8 - 2 4/15) : 3 1/2`
`=-16/5 .\frac{-15}{64} + ( 4/5 - 2 4/15) : 7/2`
`= 3/4 + \frac{-22}{15} . 2/7`
`= 3/4 + \frac{-44}{105}`
`= 139/420`