Đáp án + Giải thích các bước giải:
Xét MS : `1/199+2/198+3/197+...+198/2+199/1`
`= (1/199+1)+(2/198+1)+(3/197+1)+...+(198/2+1)+1`
`= 200/199+200/198+200/197+...+200/2+200/200`
`= 200 . (1/2+....+1/197+1/198+1/199+1/200)`
`to`
$\dfrac{ \dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{200} }{ \dfrac{1}{199}+\dfrac{2}{198}+\dfrac{3}{197}+...+\dfrac{198}{2}+\dfrac{199}{1}}$
$=\dfrac{ \dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{200} }{200 . (\dfrac{1}{2}+...+\dfrac{1}{199}+\dfrac{1}{200})}=\dfrac{1}{200}$