1/2+1/3+1/4+1/5+1/6+1/12+1/30
=1/2+1/3+1/4+1/5+1/6+1/3-1/4+1/5-1/6
=1/2+1/3+1/5+1/3+1/5
=1/2+2/3+2/5
=47/30
=1又17/30