2+0.1乘0.2+0.2乘0.2+0.3乘0.3
=2+(0.1+0.2)乘0.2+0.3乘0.3
=2+0.3乘0.2+0.3乘0.3
=2+(0.2+0.3)乘0.3
=2+0.5乘0.3
=2+0.15
=2.15