Đáp án:
`81/10`
Giải thích các bước:
`1/2`+`5/6`+`11/12`+`19/20`+ `29/30` + `41/42` + `55/56` + `71/72` + `89/90`
= `1` - `1/2` + `1` - `1/6` + `1` - `1/12` + `1` - `1/20` + `1` - `1/30` + `1` - `1/42` + `1` - `56` + `1` - `1/72` + `1` - `1/90`
= `9` - ( `1/2` + `1/6` + `1/12` + `1/20` + `1/30` + `1/42` + `1/56` + `1/72` + `1/90` )
= `9` - ( `1/1.2` + `1/2.3` + `1/3.4` + `1/4.5` + `1/5.6` + `1/6.7` + `1/7.8` + `1/8.9` + `1/9.10` )
= `9` - ( `1` - `1/2` + `1/2` - `1/3` + `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` )
= `9` - `9/10`
= `81/10`
`Honkers`
