(1-1/2+1/3-1/4+...+1/99-1/100)÷(1/102+1/104+..+1/200)=(1+1/3+..+1/99-1/2-1/4-...-1/100)÷(1/102+1/104+..+1/200)=[1+1/2+..+1/100-2(1/2+1/4+..+1/100)]÷[1/2(1/51+..+1/100)]=[1+1/2+..+1/100-(1/1+1/2+..+...