1/2+5/6+11/12+19/20.9890/9900 不是1/2+5/6+11/12+19/20.9899/990

通过裂项可得出
1/2+5/6+11/12+19/20...9890/9900
=（1-1/2)+(1-1/6)+(1-1/12)……(1-1/9900)
= 99 - (1/(1*2)+1/(2*3)……1/(99*100))
= 99 - (1-1/2+1/2-1/3……1/99-1/100)
= 99 - (1-1/100)
= 99 - 99/100
= 98又1/100
这道题我算是回答两遍了