3.14×1.9+31.4×0.81=3.14×1.9+3.14×10×0.81=3.14×(1.9+8.1)=3.14×10=31.4
3.14×1.9+31.4×0.81=31.4×0.19+31.4×0.81=(0.19+0.81)×31.4=1×31.4=31.4
