用小括号啊!
80-12.4-16.7-7.6-3.3
=80-(12.4+7.6+16.7+3.3)
=80-(20+20)
=80-40
=40
80-(12.4+16.7+7.6+3.3)=80-(12.4+7.6+16.7+3.3)=40
简便计算80-12.4-16.7-7.6-3.3=80-(12.4+7.6)-(16.7+3.3)=80-20-20=40
=80-(12.4+7.6)-(16.7+3.3)=80-20-20=40