2.9X0.45+0.29X4.2+0.029X13=0.29*4.5+0.29*4.5+0.29*1.3=0.29(4.5+4.2+1.3)=0.29*10=2.9
解:原式=0.029×45+0.029×42+0.029×13 =0.029×(45+42+13) =0.029×100 =2.9