1.9+2.99+3.999=(2-0.1)+(3-0.01)+(4-0.001)=(2+3+4)-(0.1+0.01+0.001)=9-0.111=8.889
1.9+2.99+3.999=（2-0.1）+（3-0.01）+（4-0.001）=6-（0.1+0.01+0.001）=6-0.111=5.889希望能帮到你！
