125x30x24=125x30x（8*3）=125*8*3*30=1000*90=90000
125x30x24＝125x30x3x8＝（125x8）x（30x3）＝1000x90＝90000
125x30x24=125x24x30=125x8x3x30=1000x3x30=90000
