Đáp án:
`M = 3/(3 . 5) + 3/(5 . 7) + 3/(7 . 9) + .... + 3/(95 . 97) + 3/(97 . 99)`
`-> M = 3 . [1/(3 . 5) + 1/(5 . 7) + 1/(7 . 9) + .... + 1/(95 . 97) + 1/(97 . 99)]`
`-> M = 3 . 1/2 . [1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/95 - 1/97 + 1/97 - 1/99]`
`-> M = 3/2 [1/3 + (- 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/95 - 1/97 + 1/97) - 1/99]`
`-> M = 3/2 [1/3 - 1/99]`
`-> M = 3/2 . 32/99`
`-> M =16/33`
Vậy `M = 16/33`