如图
2/5+括号6/7-1/5括回=2/5-1/5+6/7=1/5+6/7=7/35+30/35=37/35
1/35/2因为5/2-5/1-6/7+1/7=1/5-1/7=/35+30/35=32/35所以=1/2/35