原式==2.3×(1-0.9)+2.9×0.9=2.3-2.3×0.9+2.9×0.9=2.3+0.9×(2.9-2.3)=2.3+0.9×0.6=2.3+0.54=2.84
原式=(2.9-0.6)×0.1+2.9×0.9=2.9×0.1+2.9×0.9-0.6×0.1=2.9-0.06=2.84
2.3×0.1+2.9×(1-0.1)=2.3×0.1+2.9-2.9×0.1=(2.3-2.9)×0.1+2.9=2.84