12.5*8=100 12.5*0.4=5 100+5=105
12.5x(8+0.4)=12.5× 8+12.5×0.4=100+5=105
拆开来算 12.5×8+12.5×0.4=100+5=105
=12.5*8+12.5*0.4=100+5=105
