Đáp án `+` Giải thích các bước giải`:`

Ta có`:`

`A=1/3+1/2.4+1/3.5+1/4.6+....+1/198.200+1/199.201+1/2.201`

`2A=2/1.3+2/2.4+2/3.5+2/4.6+....+2/198.200+2/199.201+2/2.201`

`2A=1-1/3+1/2-1/4+1/3-1/5+1/4-1/6+...+1/198-1/200+1/199-1/201+1/201`

`2A=1+1/2+(1/3-1/3)+(1/4-1/4)+(1/5-1/5)+(1/6-1/6)+...+(1/199-1/199)+(1/201-1/201)-1/200`

`2A=3/2-1/200`

`2A=299/200`

`A=299/200:2`

`A=299/400`

Vậy `...`