1又10分之1+3又40分之1+5又88分之1+7又154分之1+9又238分之1+11又340分之1
=1+1/(2*5)+3+1/(5*8)+5+1/(8*11)+7+1/(11*14)+11+1/(14*17)+11+1/(17*20)
=1+3+5+7+9+11+1/3*(1/5-1/8+1/8-1/11+1/11-1/14+1/14-1/17+1/17-1/20)
=36+1/3*3/20
=36又1/20