1/2+5/6+11/12+-------+109/110=1-1/2+1-1/6+1-1/12+-------+1-1/110=10-(1/2+1/6+1/12+------+1/110)=10-(1-1/2+1/2-1/3+1/3-1/4+-------+1/10-1/11)=10-(1-1/11)=10-10/11=9又1/11