（1）9.81X9.8
=9.81×（10-0.2）
=98.1-1.962
=96.138
（2）0.027+9.9X0.27
=0.027+99×0.027
=0.027×（1+99）
=0.027×100
=2.7
（3）13.4-0.4X3
=13.4-1.2
=12.2