1.99*9.9
=(2-0.01)*(10-0.1)
=20-0.2-0.1+0.001
=20.001-0.3
=19.701能说下0.2、0.1、0.001是怎么算出来的吗1.99*9.9=(2-0.01)*(10-0.1)=2*10-2*0.1-0.01*10+(-0.01)*(-0.1)=20-0.2-0.1+0.001=20.001-0.3=19.701