Đáp án:
`b) \ \ 5`
`d) \ \ 1/3`
Giải thích các bước giải:
`b)`
`(-7)/9 . 4/11 + (-7)/9 . 7/11 + 5 7/9`
`= (-7)/9 . ( 4/11 + 7/11 ) + 5 + 7/9`
`= (-7)/9 . 1 + 5 + 7/9`
`= [ (-7)/9 + 7/9 ] + 5 `
`= 0 + 5 = 5`
`d)`
`( 21/31 + 2013/6039 ) - ( 44/53 - 10/31 ) - 9/53`
`= 21/31 + 2013/6039 - 44/53 + 10/31 - 9/53`
`= ( 21/31 + 10/31 ) - ( 44/53 + 9/53 ) + 2013/6039`
`= 31/31 - 53/53 + 1/3`
`= 1 - 1 + 1/3`
`= 0 + 1/3 = 1/3`
