Giải thích các bước giải:
`a)`
`(2 1/4 + 1 1/3)(2 1/3 - 1 1/4)`
`= (9/4 + 4/3)(7/3 - 5/4)`
`= (27/12 + 16/12)(28/12 - 15/12)`
`= 43/12 . 13/12`
`= /144`
`b)`
`(17/5 + 3/4)(-1/2 + (-4)/3)`
`= (68/20 + 15/20)(-3/6 - 8/6)`
`= 83/20 . (-11/6)`
`= -913/120`
`c)`
`(1/5 - 2/3) : 4`
`= (3/15 - 10/15) : 4`
`= (-7/15) . 1/4`
`= -7/60`
`d)`
`(2 1/2 + 3) : (-1/3 + 2/5)`
`= (5/2 + 6/2) : (-5/15 + 6/15)`
`= 11/2 . 15`
`= 165/2`