`\color{#FFD700}{\text{♡}}` `\color{#FFD700}{\text{v}} \color{#FFE066}{\text{i}} \color{#FFEB99}{\text{t}} \color{#FFF3B0}{\text{c}} \color{#FFF8DC}{\text{t}} \color{#FFFFF0}{\text{e}}`

Đáp án+Giải thích các bước giải:

`\text{Ta có:}` `S = 1 - 11/6 + 19/12 - 29/20 + 41/30 - 55/42 + 71/56 - 89/72 + 109/90`

`S = 1 - (1 + 1/2 + 1/3) + (1 + 1/3 + 1/4) - (1 + 1/4 + 1/5) + (1 + 1/5 + 1/6) - (1 + 1/6 + 1/7) + (1 + 1/7 + 1/8) - (1 + 1/8 + 1/9) + (1 + 1/9 + 1/10)`

`S = 1 - 1 - 1/2 - 1/3 + 1 + 1/3 + 1/4 - 1 - 1/4 - 1/5 + 1 + 1/5 + 1/6 - 1 - 1/6 - 1/7 + 1 + 1/7 + 1/8 - 1 - 1/8 - 1/9 + 1 + 1/9 + 1/10`

`S = 1 - 1/2 + 1/10`

`S = 10/10 - 5/10 + 1/10`

`S = 6/10`

`S = 3/5`

`\text{Vậy}` `S=3/5`