0.8+0.88+0.888+0.8888+0.2222=0.8+0.88+0.888+0.8888+0.2+0.02+0.002+0.0002=(0.8+0.2)+(0.88+0.02)+(0.888+0.002)+(0.8888+0.0002)=0.9+0.9+0.89+0.889=0.9+0.9+0.9-0.01+0.9-0.011=0.9×4-0.021=3.6-0.021=3.579