(1+1/2x5)+(3+1/5x8)+(5+1/8x11)+(7+1/11x14)+(9+1/14x17)+(11+1/17x20)=(1+3+5+7+9+11)+1/3×（1/2-1/5+1/5-1/8+1/8-1/11+1/11-1/14+1/14-1/17+1/17-1/20）=36+1/3×（1/2-1/20）=36×1/3×9/20=36+3/20=36又3/20
