Đáp án:

 `C=23/30`

Giải thích các bước giải:

 `C=1-\frac{1}{3xx4}-\frac{1}{4xx5}-\frac{1}{6xx7}-\frac{1}{7xx8}-\frac{1}{8xx9}-\frac{1}{9xx10}`

`=1-(\frac{1}{3xx4}+\frac{1}{4xx5}+\frac{1}{6xx7}+\frac{1}{7xx8}+\frac{1}{8xx9}+\frac{1}{9xx10})`

`=1-(1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10)`

`=1-(1/3-1/10)`

`=1-7/30`

`=30/30-7/30`

`=23/30`

Vậy `C=23/30`