用交换律简算原式＝11.18+1.82-（0.2+0.8）＝13-1＝12
11.18-0.2+1.82-0.8=(11.18+1.82)-(0.2+0.8)=13-1=12
11.18-0.2+1.82-0.8
=11.18+1.82-0.2-0.8...............交换律
=（11.18+1.82）-（0.2+0.8）...
=13-1
=12
