（1）[(35/6-49/12+63/20-77/30+91/42-105/56)]/1/8 =[(5/6-7/12+9/20-11/30+13/42-15/56)×7×8=[1/2+1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/6-1/7-1/8]×56=[1/2-1/8]×56=3/8×56=21