3.21×8.2+87×0.18+0.82×54.9 =3.21×8.2+8.7×(10-8.2)+8.2×5.49=(5.49+3.21)×8.2+8.7×10-8.7×8.2=8.7×8.2+8.7×10-8.7×8.2=87321.321÷321×3.21=321.321÷(321÷3.21)=321.321÷100=3.21321