Đáp án:

 `35/74`

Giải thích các bước giải:

 `1/6+4/21+1/56+\frac{9}{136}+\frac{8}{425}+\frac{12}{925}`

`=\frac{1}{2xx3}+\frac{4}{3xx7}+\frac{1}{7xx8}+\frac{9}{8xx17}+\frac{8}{17xx25}+\frac{12}{25xx37}`

`=1/2-1/3+1/3-1/7+1/7-1/8+1/8-1/17+1/17-1/25+1/25-1/37`

`=(1/2-1/37)+(1/3-1/3)+(1/7-1/7)+(1/8-1/8)+(1/17-1/17)+(1/25-1/25)`

`=37/74-2/74+0+0+0+0+0`

`=35/74`