1.25×8.6+7.6乘0.86=12.5×0.86+7.6×0.86=（12.5+7.6）×0.86=20.1×0.86=20×0.86+0.1×0.86=17.2+0.086=17.286
1.25×8.6+7.6×0.86=1.25×8.6+0.76×8.6=(1.25+0.76)×8.6=(2+0.01)×8.6=2×8.6+0.01×8.6=17.2+0.086=17.286
