1.25x0.64x2.5x0.5＝1.25*0.8*0.2*4*2.5*0.5＝(1.25*0.8)*(0.2*0.5)*(4*2.5)＝1
1.25*0.64*2.5*0.5=2.5*0.5*0.8*0.8*2.5*0.5=0.5*2*0.5*2=1
1.25×0.64×2.5×0.5＝1.25×0.8×0.8×2.5×0.5＝（1.25×0.8）×2.5×（0.8×0.5）＝1×2.5×0.4＝1
