Question

这道题求简便算法

Answer 1

99.9×98+0.2×999=99.9×(98+2)=99.9×100=9990

追答

已发

Answer 2

99.9x98+0.2×999
=99.9×98+2x99.9
=99.9x(98+2)
=99.9×100
=9990

Answer 3

额

Answer 4

。