Đáp án:B=1/1.2+1/3.4+1/5.6+...+1/99.100
=1‐1/2+1/3‐1/4+1/5‐1/6+...+1/99‐1/100
=﴾1+1/3+1/5+...+1/99﴿‐﴾1/2+1/4+1/6+...+1/100﴿
=﴾1+1/2+1/3+1/4+1/5+1/6+...+1/99+1/100﴿‐2﴾1/2+1/4+1/6+...+1/100﴿
=﴾1+1/2+1/3+1/4+...+1/100﴿‐﴾1+1/2+1/3+..+1/50﴿
=1/51+1/52+1/53+..+1/100 ﴾1﴿
A=1/51+1/52+1/53+..+1/100 ﴾2﴿
Từ ﴾1﴿,﴾2﴿=> A/B=1