1+3又1/6+5又1/12+7又1/20+9又1/30
=1+3+5+7+9+1/6+1/12+1/20+1/30
=1+9+3+7+5+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6
=10+10+5+1/2-1/6
=25+1/3
=25又1/3