0.45+0.25×2+0.8=（0.2+0.25）+0.25×2+0.8=（0.2+0.8）+0.25×3=1+0.75=1.75
0.45+0.25×（2+0.8）=0.45+0.25×2+0.25×0.8=0.45+0.5+0.2=1.15
