12.2+7.8-12.2+7.8的简便运算:12.2+7.8-12.2+7.8=12.2-12.2+7.8+7.8=(12.2-12.2)+(7.8+7.8)=0+15.6=15.6
12.2+7.8-12.2+7.8=(12.2-12.2)+(7.8+7.8)=0+15.6=15.6
12.2+7.8-12.2+7.8=12.2-12.2+7.8+7.8=15.6
=(12.2-12.2)+(7.8+7.8)=0+15.6=15.6