8x(0.4+12.5)ⅹ5=8x0.4X5+8乂12.5X5=8x(0.4X5)+(8X12.5)x5=8ⅹ2十100ⅹ5=16+500=516
8×(0.4+12.5)×5=8×0.4×5+8×12.5×5=8×2+100×5=16+500=516
8*(0.4+12.5)*5=40*(0.4+12.5)=40*0.4+40*12.5=16+500=516