原式=6.4×12.5×0.5÷1.6÷0.5=6.4÷1.6×12.5×0.5÷0.5=4×12.5×1=50
6.4×12.5×0.5÷(1.6×2.5×0.2)=12.5*8*0.8*0.5/(2.5*4*0.4*0.2)=40/0.8=500
