九九乘以一百分之五十七的简便方法？99x(57/100)=99x0.57=56.43
99x57/100=(100x57/100)一1x57/100=57-57/100=56又43/100=56.43
99×57/100=（100-1）×57/100=100×57/100-1×57/100=57-57/100=56又43/100
