（1）4.05÷0.81+2.4=5+2.4=7.4；（2）0.389×4×0.25=0.389×（4×0.25）=0.389×1=0.389；（3）4.02×3.02+4.02×6.98=4.02×（3.02+6.98）=4.02×10=40.2；（4）0.6×[25-（8.7-3.7）]=0.6×[25-5]=0.6×20=12．
