=1+1/12+1+1/20+1+1/30+1+1/42+1+1/56
=5+1/12+1/20+1/30+1/42+1/56
=5+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8
=5+1/3-1/8
=5又5/24