7/6+ 13/12+ 21/20 +3l/3o +43/42 +57/56 +73/72 +91/90=(1+1+1...+1)+(1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)=8+(1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10)=8+(1/2-1/10)=8+2/5=8又5分之2
