6/1+12/1+20/1+30/1+42/1+56/1+72/1 =(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+.+(1/8-1/9) =1/2-1/9 =7/18 10/1+3又40/1+5又88/1+9又154/1+11又238/1 =3+5+9+11+1/10+1/40+1/88+1/154+1/238 =28+[(1/2-1/5)+(1/5-1/8)+(1/8-1/11)+(1/11-1/14)+(1/14-1/17)]÷3 =28+(1/2-1/17)÷3 =28+5/34 =28又34分之5