7.48+3.17-(2.48-6.83)
=7.48+3.17-2.48+6.83
=（7.48-2.48）+（3.17+6.83）
=5+10
=15
3.6*11.1+1.2*66.7
=1.2*3*11.1+1.2*66.7
=1.2*33.3+1.2*66.7
=1.2*(33.3+66.7)
=1.2*100
=120
12.8*34.5+12.8*12.3+46.8*87.2
=12.8*(34.5+12.3)+46.8*87.2
=12.8*46.8+46.8*87.2
=46.8*(12.8+87.2)
=46.8*100
=4680
问题补充：
7.2*14.5+17*2.8
=7.2*（17-2.5）+17*2.8
=7.8*17-72*0.25+17*2.8
=17*（7.8+2.8）-72÷4
=17*10-18
=170-18
=152
【 8 4/3】-.35+(【1 4/1】-【6 20/13】）
=8.75-.35+1.25-6.65
=(8.75+1.25)-(6.65+0.35)
=10-7
=3